Unusable rhymes with:
excusable, fusible, inexcusable, usable, excusable, fusible, inexcusable, reusable, usable, advisable, analyzable, disposable, divisible, excusable, exercisable, feasible, fusible, implausible, inadvisable, inexcusable, infeasible, invisible, plausible, realizable, recognizable, reusable, sizable, sizeable, unfeasible, unrecognizable, usable, visible
Unusable sounds like:
uncivil, uncouple, unmanageable, unshakable, unshakeable, unsuccessful, unsuccessfully