Or search: ascertain
2 Syllables: SU
airing, Baring, bearing, caring, chairmen, Charing, daring, erring, flaring, glaring, herring, larynx, pairing, paring, pharynx, sharing, sparing, squaring, staring, swearing, tearing, wearing
3 Syllables: USU
comparing, declaring, despairing, forbearing, impairing, preparing, repairing, unerring, unsparing
4 Syllables: UUSU
overbearing

Found 32 words across 3 groupings. Skipped 2 excess words of a similar stem.