Or search: pupil, hearer, audience, beholder, listener, observer, educatee, attender, perceiver, accountant, controller, percipient, comptroller
2 Syllables: SU
foreigner
3 Syllables: SUU
commoner, gossamer, monitor, officer, oftener, Oliver
4 Syllables: SUUU
kilometers
4 Syllables: USUU
astrologer, astronomer, biographer, geographer, idolaters, philosopher, photographer, thermometer
4 Syllables: UUSU
kilometres

Found 17 words across 5 groupings. Skipped 12 excess words of a similar stem.