Or search: unrelated, extraneous, immaterial, irrelevant, impertinent, rectangular, perpendicular
3 Syllables: SUU
audible, doctrinal, doggerel, laudable, nautical, nominal, optional, plausible, possible, probable, proximal, topical, volatile
4 Syllables: USUU
abdominal, apocryphal, canonical, impossible, improbable, inaudible, inaugural, methodical, phenomenal
5 Syllables: UUSUU
inexhaustible
6 Syllables: UUUSUU
anthropological, etymological

Found 25 words across 4 groupings.