11 letters · 17 points in Scrabble
adjective resistant to penetration by grease or oil or wax
originEtymology tree Vulgar Latin crassus~grassus Proto-Indo-European *-yós Proto-Italic *-ios Old Latin -ios Vulgar Latin -ius Vulgar Latin -ia Vulgar Latin *crassia Anglo-Norman grecebor. Middle English grece English grease English -proof English greaseproof From grease + -proof.
Etymology from Wiktionary, CC BY-SA 3.0