Stiffens rhymes with:
gryphons, dolphins, dolphins', entoffen's, gryphons, muffins, orphans, siphons, softens, steffens, stephans, toughens
Stiffens sounds like:
skydiving, stabbing, stabbings, staffing, staving, stebbins, steepness, stefani's, stefaniak, stefanic, stefanich, stefanick, stefanik, stefanko, stefanowicz, stefanski, steffanci, steffens, stepanek, stepanian's, stepanski, stephans, stephen's, stephens, stephens's, stepping, steven's, stevens, stevens', stevens's, stiffening, stiffness, stooping, stopping, stubbins, stuffing, suggestiveness