Or search: thief, stealer
2 Syllables: SU
Berger, Berkshire, Bernard, Burger, burgher, burner, courier, earlier, earner, earthworks, fervor, firmer, further, girders, Herbert, Herder, learner, Mercer, merger, murder, murmur, nurture, perjured, pervert, searcher, sterner, Turner, Turner's, Werner, Wordsworth, worker, worthier
3 Syllables: USU
disturbers, observer, precursor, preserver, usurper

Found 37 words across 2 groupings. Skipped 17 excess words of a similar stem.