Hardest rhymes with:
weirdest, blondest, buddhist, coldest, eldest, encyclopedist, fondest, grandest, kindest, loudest, methodist, mildest, modest, oddest, oldest, orthopedist, prejudiced, propagandist, proudest, rudest, saddest, sadist, shrewdest, soundest, stupidest, weirdest, widest
Hardest sounds like:
hardesty, hardgood, hardiest, hardisty, heartiest