• Etymology Today from M-W: oleaginous \oh-lee-ADGE-uh-nuss\
1 : resembling or having the properties of oil : oily; also : containing or producing oil
*2 : marked by an offensively ingratiating manner or quality

The oily "oleaginous" slipped into English through Middle French, coming from the Latin "oleaginus," meaning "of an olive tree." "Oleaginus" came from the Latin "olea," meaning "olive tree," and ultimately from the Greek "elaia," meaning "olive."
"Oleaginous" was at first used in a literal sense, as it still can be. An oleaginous substance is simply oily, and an oleaginous plant produces oil. The word took on its extended "ingratiating" sense in the 19th century.
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