Similar word to unusable:

abortive, bootless, counterproductive, disadvantageous, dysfunctional, expendable, feckless, fruitless, futile, good-for-nothing, hopeless, idle, impracticable, impractical, incompetent, ineffective, ineffectual, inept, inoperative, inutile, meaningless, no good, nonfunctional, of no use, pointless, profitless, purposeless, scrap, stupid, unavailable, unavailing, unfunctional, unproductive, unprofitable, unpurposed, unusuable, unworkable, vain, valueless, waste, weak, worthless