Underused rhymes with:
overused, abused, accused, amused, bemused, confused, defused, diffused, disabused, excused, fused, infused, misused, mused, overused, recused, refused, suffused, transfused, unused, used
Underused sounds like:
unaddressed, unauthorized, undercoat, undercooked, undercut, underside, undersized, understate, understated, understood, understudy, underweight, underweighted, undressed, uninterested