-logy repr. F. -logie, medL. -logia, Gr. -logíā, which is partly f. lógos discourse, speech, partly f. log-, var. of leg-, légein speak; hence derivs. in -logia mean either
1.. saying or speaking in such-and-such a way, as eulogy, tautology, or

2.. the science or study with which a person (designated by -logos -LOGIST, -LOGER, etc.) is concerned, or that deals with a certain subject. Of the latter class, the first el. is a sb. and in combination ends in o, so that the regular form of such words is in -ology; an exception is MINERALOGY. Mod. formations in logy imply correl. formations in -logical, formerly also, now rarely, -logic (F. -logique, L. -logicus, Gr. -logikós), and -logist (see prec.).

-logy (-ology) combining form denoting field of study.