Or search: keen, acute, incisive, knifelike, lancinate, perceptive, penetrating, discriminating
2 Syllables: SU
cheering, clearing, earrings, fearing, gearing, hearing, jeering, nearing, peering, rearing, shearing, sneering, steering, syringe, tearing
3 Syllables: USU
adhering, appearing, endearing, reappearing
4 Syllables: UUSU
disappearing, domineering, engineering, interfering, persevering, pioneering, volunteering
5 Syllables: UUUSU
electioneering

Found 27 words across 4 groupings. Skipped 2 excess words of a similar stem.