"Ethology" is a word that has multiple meanings even though they all derive from the same Greek root meaning to depict character or habit. The earliest one, according to the Oxford English Dictionary, is "the portrayal of character by mimic gestures: mimicry." This sense is very definitely obsolete, though, as is the meaning "a treatise on manners or morals."

The scientific meaning used earlier in English, as the Webster 1913 entry indicates, is from John Stuart Mill's 1843 book System Of Logic, 'where he proposed the development of a new science he called "ethology," whose purpose would be the explanation of individual and national differences in character, on the basis of associationistic psychology.' (Raymond E. Fancher, Editor, Journal of the History of the Behavioral Sciences, as quoted in AWADmail)

The second scientific sense of the word, the study of animal behavior, comes from the French "éthologie," which was coined by zoologist Isidore Geoffroy Saint-Hilaire (1805-1861). The word seems to date from 1859 in French; the OED gives its first appearance in English in this sense as 1897. Its French originator advocated studying animals in their natural habitats, which was apparently an unusual idea for the time.

A.Word.A.Day 1 February 2002 and a followup in the weekly "AWADmail" Issue 66 of 3 February 2002
Oxford English Dictionary entry for "ethology"