Atheism and atheist are forgiving words. The speaker may be referring to
- believing in the nonexistence of a god, or
- not believing in (doubting) the existence of a god, which is different, or
- estrangement from or disobedience of a god which exists,
depending on context, including the speaker’s own beliefs. This is true, not just of usage in the modern era, but clear back to the 16th century when the words were first borrowed from French.
Being estranged from a god which exists was the original meaning. The term atheist wasn’t invented by atheists ; it was invented by religious believers as an epithet (a disparaging word). It literally means “without god”, and was used to characterize people who denied the gods or were estranged from the gods in some way. The religious still sometimes use it in this sense.
Atheists co-opted the word in the way that Americans co-opted the term Yankee. Subsequently, the meaning of the term mutated quite a bit, as people argued over time about the existence of a god and what you can know about it.
Some dictionary entries are so short that they lose the nuances of meaning of these words. Unabridged dictionaries and scholarly articles are better guides.
The best hope you have when you hear either term is that the person using it defines it in context. That is also the best thing to do when you use it yourself.
“atheism”, A New English Dictionary On Historical Principles, Vol 1, A and B. This work is in the public domain. As it is not an easily searchable source, I have transcribed the relevant entries in full :
Atheism (ēⁱ·þiˌiz’m). Also 6 athisme. [a. F. athéisme (16th c. in Littré), f. Gr. ἄθεος : see Aᴛʜᴇᴀʟ and -ɪꜱᴍ. Cf. It. atheismo and the earlier Aᴛʜᴇᴏɴɪꜱᴍ.]
Disbelief in, or denial of, the existence of a God.
Also, Disregard of duty to God, godlessness (practical atheism).
1587 Gᴏʟᴅɪɴɢ De Mornay xx. 310 Athisme, that is to say, vtter godlesnes.
1605 Bᴀᴄᴏɴ Adv. Learn. ɪ. i. § 3 A little or superficial knowledge of philosophy may incline the mind of man to atheism.
1711 Aᴅᴅɪꜱᴏɴ Spect. No. 119 ⁋ 5 Hipocrisy in one Age is generally succeeded by Atheism in another.
1859 Kɪɴɢꜱʟᴇʏ Lett. (1878) II. 75 Whatever doubt or doctrinal Atheism you and your friends may have, don’t fall into moral Atheism.
Atheist (ēⁱ·þiˌist). Also 6 atheyst, 6–7 athist(e. [a. F. *athéiste (16th c. in Littré), or It. atheista : see prec. and -ɪꜱᴛ.]
1. One who denies or disbelieves the existence of a God.
[a 1568 Cᴏᴠᴇʀᴅᴀʟᴇ Hope of Faithf. Pref. Wks. II. 139 Eat we and drink we lustily ; to-morrow we shall die : which all the epicures protest openly, and the Italian atheoi.]
1571 Gᴏʟᴅɪɴɢ Calvin on Ps. Ep. Ded. 3 The Atheistes which say .. there is no God.
1604 Rᴏᴡʟᴀɴᴅꜱ Looke to it 23 Thou Damned Athist .. That doest deny his power which did create thee.
1709 Sʜᴀꜰᴛᴇꜱʙ. Charac. ɪ. ɪ. § 2 (1737) II. ɪɪ To believe nothing of a designing Principle or Mind, nor any Cause, Measure, or Rule of Things, but Chance .. is to be a perfect Atheist.
1876 Gʟᴀᴅꜱᴛᴏɴᴇ in Contemp. Rev. June 22 By the Atheist I understand the man who not only holds off, like the sceptic, from the affirmative, but who drives himself, or is driven, to the negative assertion in regard to the whole Unseen, or to the existence of God.
2. One who practically denies the existence of a God by disregard of moral obligation to Him ; a godless man.
1577 Hᴀɴᴍᴇʀ Anc. Eccl. Hist. 63 The opinion which they conceaue of you, to be Atheists, or godlesse men.
1660 Sᴛᴀɴʟᴇʏ Hist. Philos. 323/2 An Atheist is taken two ways, for him who is an enemy to the Gods, and for him who believeth there are no Gods.
1667 Mɪʟᴛᴏɴ P. L. ɪ. 495 When the Priest Turns Atheist, as did Ely’s Sons.
1827 Hᴀʀᴇ Guesses Ser. ɪ. (1873) 27 Practically every man is an atheist, who lives without God in the world.
B. attrib. as adj. Atheistic, impious.
1667 Mɪʟᴛᴏɴ P. L. ᴠɪ. 370 The Atheist crew.
1821 Lᴏᴄᴋʜᴀʀᴛ Valerino II. xi. 316 Borne from its wounded breast an atheist cry Hath pierced the upper and the nether sky.
“atheism”, The Catholic Encylopedia:
Since its first coming into use the term atheism has been very vaguely employed, generally as an epithet of accusation against any system that called in question the popular gods of the day. Thus while Socrates was accused of atheism (Plato, Apol., 26, c.) and Diagoras called an atheist by Cicero (Nat. Deor., I, 23), Democritus and Epicurus were styled in the same sense impious (without respect for the gods) on account of their trend of their new atomistic philosophy. In this sense too, the early Christians were known to the pagans as atheists, because they denied the heathen gods ; while, from time to time, various religious and philosophical systems have, for similar reasons, been deemed atheistic. … Atheism, historically considered, has meant no more in the past than a critical or sceptical denial of the theology of those who have employed the term as one of reproach, and has consequently no one strict philosophical meaning.
For there are gods : for our knowledge of them is indistinct. But they are not of the character which people in general attribute to them.
—Lucretius Carus, Laert., Life of Epicurus, XXVII
Indeed, this one citation perfectly illustrates the fundamental historic meaning of the term, atheism.
“atheism”, Concise Dictionary of Religion, Irving Hexham, 1999:
originally used in Greece of all those who, whether they believed in a god or not, disbelieved in the official gods of the State : Socrates was the classic instance. In the Roman Empire the term was applied to Christians but sometimes Christians, like Polycarp, would turn the term against their persecutors. Until the expression “agnosticism” came into general use in the nineteenth century, the term “atheism” was popularly used to describe those who thought the existence of God an unprovable thesis.
“atheism”, Free On-Line Dictionary of Philosophy 3.0, 26-03-2001:[PDF]
the belief that, or the philosophical position according to which, God, gods, deities, and supernatural powers do not exist. In this respect it is similar to secularism and opposed to any variety of theism. … Popularly, atheism is often taken to imply a lack of any ideals or values whatsoever (see immoralism), but this connotation rests on the controversial assumption that religious or supernatural values are the only real values.
“atheism”, Internet Encyclopedia of Philosophy:
negative atheism … includes someone who has never reflected on the question of whether or not God exists and has no opinion about the matter and someone who had thought about the matter a great deal and has concluded either that she has insufficient evidence to decide the question, or that the question cannot be resolved in principle. … Atheism can be narrow or wide in scope. The narrow atheist does not believe in the existence of God (an omni-being). A wide atheist does not believe that any gods exist, including but not limited to the traditional omni-God.
“atheism”, Philosophy Pages, Garth Kemerling:
Belief that god does not exist. Unlike the agnostic, who merely criticizes traditional arguments for the existence of a deity, the atheist must offer evidence (such as the problem of evil) that there is no god or propose a strong principle for denying what is not known to be true.
“atheism”, The Century Dictionary and Cyclopedia:
n. The doctrine that there is no God ; denial of the existence of God.
n. The denial of theism, that is, of the doctrine that the great first cause is a supreme, intelligent, righteous person.
n. A practical indifference to and disregard of God ; godlessness.
“atheism”, Merriam-Webster Dictionary:
1 a : a lack of belief or a strong disbelief in the existence of a god or any gods
1 b : a philosophical or religious position characterized by disbelief in the existence of a god or any gods
2 archaic : godlessness especially in conduct : ungodliness, wickedness
atheism, Webster’s Revised Unabridged, 1913 Edition:
n. 1. The disbelief or denial of the existence of a God, or supreme intelligent Being.
“atheism”, Webster’s New World College Dictionary, 4th Edition:
• The belief that there is no God, or denial that God or gods exist.
- the doctrine or belief that there is no God.
- disbelief in the existence of a supreme being or beings.
“atheism”, Collins English Dictionary:
• The belief that there is no God.
• Rejection of belief in God or gods.
“atheism”, Webster’s Dictionary, 1828:
• The disbelief of the existence of a God, or Supreme intelligent Being.
“atheism”, Webster’s New World College Dictionary:
• Disbelief in or denial of the existence of God or gods.
“atheism”, Macmillan Dictionary:
• The belief or theory that God does not exist.
“atheism”, Oxford Learner’s Dictionaries:
• The belief that God does not exist.
“atheism”, Cambridge Dictionary:
• The belief that God does not exist.