Synonyms of the word 
GREASEPROOF → IMPERVIABLE - IMPERVIOUS
greaseproof
- adj. Resistant to grease.
- v. (transitive) To make resistant to grease.
imperviable
- adj. impervious.
impervious
- adj. Unaffected or unable to be affected by.
- adj. Preventive of any penetration; impenetrable, impermeable, particularly of water.
- adj. Immune to damage or effect.
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