Oily

wiktionary

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From Middle English oylei, equivalent to oil +‎ -y. Compare German ölig(“oily”), Swedish oljig(“oily”).

etymonline

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oily (adj.)

"resembling oil, having the qualities of oil," late 14c., oilei, from oil (n.) + -y (2). Figurative meaning "smooth, unctuous" is from 1590s. Related: Oilily; oiliness.