We found one dictionary that defines the word grease one's gills:

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1. grease one's gills: Wiktionary

Definitions from Wiktionary (grease one's gills) ▸ verb:  (slang) To eat a hearty meal. ▸ Words similar to grease one's gills ▸ Usage examples for grease one's gills ▸ Idioms related to grease one's gills ▸ Wikipedia articles (New!) ▸ Words that often appear near grease one's gills ▸ Rhymes of grease one's gills ▸ Invented words related to grease one's gills