Vast rhymes with:
aghast, amassed, assed, ast, bast, blast, cast, caste, classed, fast, gassed, gast, glassed, grassed, harassed, hast, kast, lambaste, last, lymphoblast, massed, mast, miscast, nast, passed, past, precast, rast, recast, surpassed, unsurpassed
Vast sounds like:
vacate, vacated, vaguest, vajda, vashti, vasta, vaught, vegetate, vest, vesta, vested, vexed, vicissitude, viscosity, visigoth, visit, visited, vist, vista, voest, voght, vogt, voiced, voight, voigt, vojta, vouched, vought, voyaged