They seem to mean the same thing, yet when spoken they sound like the negative of each other.
What's the secret behind those two words?

  • The second word derives from "ingenuity", which geniuses sometimes have.
    – user730
    Dec 16, 2010 at 2:15

2 Answers 2


On the surface, one might think that ingenious is somehow based on the word genius. Interestingly, this is not true.

The word ingenious does not actually have the in- prefix for negation. Instead, it comes originally from the Latin ingeniōsus, which means "intellectual, talented, ingenious". At times in history it was also spelled "engenious". Indeed, ingeniōsus appears to be the same root that gave us the word engine.

Genius was originally different, but evolved to have a meaning that is similar to ingenious. It came to us from Latin, but it was originally Greek. According to the OED, it mainly had the meaning of, approximately, "genie" or similar type of spirit, in Latin. Figuratively, it was also used to mean "characteristic disposition; inclination; bent, turn or temper of mind." In English, German, and most of the Romance languages aside from Latin, it had the meaning of "natural ability" starting around the 1600s. The OED speculates that the meaning of genie was pushed towards the meaning of ingenious because of "confusion" between the two (that is, their superficial similarity).

  • Excellent explanation. Just one thing: where did you find that genius came from Greek? The major Latin dictionaries (OLD, L&S) simply say it comes from the Latin/PIE root gen-, like ingenium/-osus, and LSJ says no similar word exists in Greek. The OED doesn't say anything about a Greek origin either. May 12, 2011 at 1:04
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    @Cerberus: OED says: "< Latin genius, < *gen- root of gi-gn-ĕre to beget, Greek γίγνεσθαι to be born, come into being." So that is where I got that idea. Am I misunderstanding the OED etymology shorthand?
    – Kosmonaut
    May 12, 2011 at 3:14
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    Oh, I see. I think they'd put f. ("from") or < before Greek if they meant that it came from Greek. In your quote, they trace back the etymology to *gen-, then proceed to say that *gen- is also the root of gignere, [and of] Greek gignesthai. It is kind of stupid that they still use these awkward run-on etymologies in the digital age, and with impossible abbreviations. I am forced to look up a. every time I use the dictionary, because I just cannot remember that it means adopted from (I looked it up again just now). May 12, 2011 at 13:51
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    I had thought there was a separate notation to indicate sibling words, but I think you are right. Maybe it isn't used consistently. As for the formatting, I guess the current OED overhaul (completion date: 2037!) began back in the early 90s when book space was still a reasonable concern, and so they are probably keeping the format consistent throughout this version. It is depressing to think that, at this pace, they will never have a digitally-savvy version of the OED during our lifetimes! This is not the first time I have been confused by the super-compact way things are worded in there.
    – Kosmonaut
    May 12, 2011 at 22:36
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    Oh dear, that is sad indeed! Well, at least our children will get to live in a better world than we. May 12, 2011 at 23:41

Though in view of the answer above, I thought to quote two answers from this Reddit question which retrograde to Proto-Indo-European. I edit them lightly to improve readability.

By: user 'gnorrn', 2015 July 26

The duality goes all the way back to Latin:

  • genius meant "the tutelar deity of a person or place"
  • ingenium meant "innate or natural quality, nature"

Both words ultimately derive from the Proto-Indo-European root *ǵenh₁-
("to produce, to beget, to give birth"). The prefix in- has several meanings in Latin. Here it does not have the privative/negation meaning (cognate with English "un-"), but the meaning of "in, into".

By: user 'wurrukatte', 2015 July 26

[Originally, the querier exemplified with 1. in cantation and in carceration and 2. in genius .]

In 1 and 2, in- is not the same prefix. It is the same morpheme for two different prefixes that happened to become homophonous.
In 1, in- means "not". This in- goes back to PIE '*n̥-', which gave Germanic languages like English the prefix 'un-'.
In 2, the other prefix in- is actually a preverb going back to PIE *h₁en, "in, into", which gave Germanic *in > English 'in', "in, within".

In Latin, both PIE forms resulted in the form 'in(-)'. In other languages, they didn't necessarily become homophones, just as in English, like Ancient Greek 'a(n)-' and 'en-'.

English also has two homophonous prefixes that mean different things: 'un-' meaning 'not', as said, goes back to PIE '*n̥-'.

In contrast, 'un-' can also mean "reversal , opposite" as used with verbs like 'undo', 'unlike'. This goes back to Old English 'an(d)-', from Proto-Germanic *and-, from PIE *h₂enti-.
This 'un-' is cognate with Ancient Greek 'anti-' and Latin 'ante'.

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