adj. 25B6; adjective
a watertight container : IMPERMEABLE, impervious, (hermetically) sealed; waterproof, water-repellent, water-resistant, damp-proof.
a watertight alibi : INDISPUTABLE, unquestionable, incontrovertible, irrefutable, unassailable, impregnable; foolproof, sound, flawless, airtight, conclusive.
leaky, flawed.