Or search: restful, relaxing, slumbrous, slumberous
1 Syllable: S
Crowell, Joel, Lowell
2 Syllables: SU
boastful, coastal, doleful, focal, global, hopeful, jovial, local, mobile, modal, Mogul, noble, opal, oval, postal, social, total, vocal, Vogel, woeful
2 Syllables: US
bestowal
3 Syllables: USU
baronial, betrothal, colloquial, colonial, disposal, ennoble, ignoble, immobile, parochial, proposal, reproachful, unsocial
4 Syllables: UUSU
anecdotal, antisocial, ceremonial, matrimonial, sacerdotal, testimonial
5 Syllables: UUUSU
Constantinople

Found 43 words across 6 groupings. Skipped 8 excess words of a similar stem.