I have always wondered about the similarity of the two words

Astronomy and Astrology

that describe two very different things but have their beginning in common and are sometimes confused in everyday language. The linguistic difference (if one can say so) between them is only in the endings '-onomy' and '-ology'. Two further examples are

Topology and Topography

Geology and Geography

where now we have the endings '-ology' and '-ography'.

  • What are the meanings of the different endings '-onomy', '-ology' and '-ography' ?

  • I would also be curious about whether it is a coincidence that '-ology' appears in all the examples above? Does it maybe have historical reasons?

  • And furthermore, are there more such pairs to be found? (I can't think of any others)

  • economy, ecology; biology, biography; cardiography, cardiology; gastronomy, gastrology;
    – Mitch
    Commented Jun 13, 2013 at 0:17
  • I thought examples might be useful. geology: body of knowledge about the earth (rocks: where they are and why they are) geography: writing about the earth (observations) geometry: measurement (surveying) geonomy: "...physical laws relating to the earth, including geology and physical geography ..." wordnik.com/words/geonomy Thanks for the previous posts.
    – user54661
    Commented Oct 22, 2013 at 10:35
  • I've had this question for quite some time, and never thought it would attract so enlightening answers and comments.
    – 0xc0de
    Commented Oct 30, 2017 at 7:34

1 Answer 1


The suffix -logy means a branch of learning, or study of a particular subject.

The suffix -nomy means a system of rules or laws, or body of knowledge of a particular subject.

These two are often intertwined as you might expect.

(Note that -ology and -onomy are alternate forms which include the connecting vowel -o-.)

The suffix -graphy refers to something written about a particular subject.

It's no coincidence that -logy- appears to be so common, as it refers to a wide variety of branches of study.

Another familiar suffix is -metry which refers to measurement, e.g. geometry, to continue your geo- theme.

  • 9
    Greek ΓΡΆΦΩ /'grapʰɔ:/ 'write'; ΛΌΓΟΣ /'logos/ 'word'; ὊΝΟΜΑ /'onoma/ 'name; rule'. So -ography means 'writing about', ology means 'words about', and -onomy means 'rules about'. Commented Jun 12, 2013 at 23:06
  • From: dictionary.reference.com/browse/-rama?s=t -rama: variant of -orama, occurring as the final element in compounds when the first element is disyllabic and does not end in -r, used so that the entire word maintains the same number of syllables as panorama, Cinerama, and telerama. Word origin & History of -rama: noun suffix meaning "spectacular display or instance of," 1824, abstracted from panorama, ultimately from Gk. horama "sight." [So it appears that -orama means "about sight," if Mr. Lawler is correct (which I assume he is).] Commented Jun 12, 2013 at 23:40
  • As an "armchair etymologist" I might have been tempted to suppose that -nomy had its origins in nemein -> nomos -> name. In which case arguably astronomers and astrologers have got their names mixed up, since the former really do study the stars in a meaningful sense. Astrologers are more concerned with assigning names to "accidental configurations" in the night sky that just happen to have a particular appearance from our vantage point. Commented Jun 13, 2013 at 0:09
  • @FumbleFingers, is astrophysicist a preferred term these days? Just wonderin' Commented Jun 13, 2013 at 0:17
  • 4
    @JohnLawler: Astronomy and economics are not from onoma "name" but from nomos "law". And I don't think onoma can mean "rule". You knew I couldn't resist. Commented Oct 25, 2014 at 8:10

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