Shrewdest rhymes with:
rudest, buddhist, rudest, blondest, buddhist, coldest, eldest, encyclopedist, fondest, grandest, hardest, kindest, loudest, methodist, mildest, modest, oddest, oldest, orthopedist, prejudiced, propagandist, proudest, rudest, saddest, sadist, soundest, stupidest, weirdest, widest
Shrewdest sounds like:
scratched, securitized, shortcut, shortest, shortsighted