'watertight' definitions:

Definition of 'watertight'

From: WordNet
adjective
Not allowing water to pass in or out
adjective
Without flaws or loopholes; "an ironclad contract"; "a watertight alibi"; "a bulletproof argument" [syn: unassailable, unshakable, watertight, bulletproof]

Synonyms of 'watertight'

From: Moby Thesaurus