Meaning of ‘-onomy’, ‘-ology’ and ‘-ography’

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)


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.

Source : Link , Question Author : alexlo , Answer Author : Stuart Allen

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