Impossible to quench:
— Unquenchable thirst.

synonym: quenchless.

Roget 159: strong, mighty, vigorous, forcible, hard, adamantine, stout, robust, sturdy, hardy, powerful, potent, puissant, valid.    resistless, irresistible, invincible, proof against, impregnable, unconquerable, indomitable, dominating, inextinguishable, unquenchable; incontestable; more than a match for; overpowering, overwhelming; all powerful, all sufficient; sovereign.    able-bodied; athletic; Herculean, Cyclopean, Atlantean^†; muscular, brawny, wiry, well-knit, broad-shouldered, sinewy, strapping, stalwart, gigantic.    manly, man-like, manful; masculine, male, virile.    unweakened^†, unallayed, unwithered^†, unshaken, unworn, unexhausted^†; in full force, in full swing; in the plenitude of power.    stubborn, thick-ribbed, made of iron, deep-rooted; strong as a lion, strong as a horse, strong as an ox, strong as brandy; sound as a roach; in fine feather, in high feather; built like a brick shithouse; like a giant refreshed.    ... show more

Roget 817a: greedy, avaricious, covetous, acquisitive, grasping; rapacious; lickerish^†.    greedy as a hog; overeager; voracious; ravenous, ravenous as a wolf; openmouthed, extortionate, exacting, sordid^†, alieni appetens [Lat.]; insatiable, insatiate; unquenchable, quenchless; omnivorous.    ... show more