watertight Get Printable Handwriting (wa-ter-tight) 3 syllables Learn It! Spelling Test Definition adjective. 1 constructed so tightly that water cannot enter or leave 2 leaving no flaws ambiguities or possibilities for evasion; a watertight plan Example Sentence The ship is watertight. Synonyms water cannot enter; water cannot leave; no flaws Antonyms leaky; flawed Share with your friends: