watertight vs unassailable

watertight and unassailable both are adjectives.

Word	Noun	Adjective	Verb	Adverb
watertight	No	Yes	No	No
unassailable	No	Yes	No	No

As adjectives, watertight and unassailable are synonyms defined as:

Other synonyms of watertight include bulletproof, ironclad, unshakable.

watertight (adjective)	unassailable (adjective)
without flaws or loopholes	without flaws or loopholes
not allowing water to pass in or out	impossible to assail
	immune to attack; incapable of being tampered with