4 Syllablescandescently, excrescently, fluorescently, incessantly, quiescently
Now you can make multisyllabic rhymes in the new rhymit app :)
5 Syllablesacquiescently, adolescently, arborescently, convalescently, effervescently, evanescently, incandescently, iridescently, obsolescently, opalescently