Here's what rhymes with sponlaneous.
instantaneous Words that almost rhyme with sponlaneous
gaseous habeas canniness happiness pancreas malleolus dalliance transience patchiness tackiness palliates valiance bagginess brassiness chattiness glassiness shagginess classiness cragginess fattiness faddiness nattiness sappiness transients nastiness craftiness scantiness pantheists retaliates bassinets scratchiness snappiness draftiness ghastliness bathyscaphs