Or search: dire, awful, dread, dreaded, fearful, alarming, fearsome, horrific, atrocious, abominable, horrendous, frightening, unspeakable, disagreeable
2 Syllables: SU
Eccles, Federal, fretful, Hegel, kettle, medal, meddle, metal, mettle, nettle, pebble, pedal, petal, rebel, settle, speckled, spectral, treble
3 Syllables: USU
Ezekiel, forgetful, neglectful, projectile, respectful, unsettled
4 Syllables: UUSU
disrespectful

Found 25 words across 3 groupings. Skipped 12 excess words of a similar stem.