Unsolvable rhymes with:
solvable, solvable, solvable, achievable, approvable, believable, conceivable, drivable, forgivable, immovable, inconceivable, livable, lovable, microwavable, movable, observable, provable, receivable, removable, solvable, survivable, unbelievable, unforgivable, unlivable
Unsolvable sounds like:
unassailable, unsalable, unsaleable