Somnolence rhymes with:
ambivalence, ambulance, benevolence, equivalence, excellence, insolence, nonviolence, opulence, pestilence, petulance, prevalence, turbulence, vigilance, violence, virulence
Somnolence sounds like:
scanlon's, schmeling, signaling, signalling, smalling, smallness, smelling, smiling, smolensk, smolenski, smolinski, smolinsky, snelling, snellings, somalians