In a manner that is greasy or slippery; in a way that leaves grease or oil.
From 'grease' (Old French 'graisse' from Latin 'crassus' meaning thick/fat) + '-ably' (suffix forming adverbs). The word combines the adjective form with an adverbial suffix to create an adverb of manner.
This is an extremely rare word that seems to exist in some dictionaries but is barely used in modern English—most people would just say 'in a greasy way' instead. It's a perfect example of how English allows us to theoretically add '-ably' to almost any adjective, but many such combinations never actually catch on in real speech.
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