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