-proof

From the adjective proof (“fully resistant”), from the same Old French root as prove.

-proof

1. Added to a noun to form an adjective denoting imperviousness to that noun.
2. Added to a noun to form a verb denoting a process to make something impervious to that noun.

• Often used as the second part of a combined form (such as bullet-proof) rather than as a true suffix (as in waterproof)

• -safe

• OPFOR