Here's what rhymes with gainful.
                        
                        
                    
                                painful  baneful  disdainful  Words that almost rhyme with gainful
shameful  angel  anal  able  cable  faithful  grateful  graceful  cranial  fateful  hateful  gable  baleful  wakeful  pailful  table  fatal  label  naval  racial  basal  facial  nasal  cradle  fable  glacial  papal  maple  playful  wasteful  hazel  natal  navel  sable  archangel  ladle  tasteful  bagel  plateful  bacchanal  laetrile  pailsful  enable  stable  unable  spatial  staple  ungrateful  unfaithful  ungraceful  flavourful  felafel  appraisal  disgraceful  disable  palatial  biracial  worktable  relabel  singable  unstable  betrayal  neonatal  distasteful  prenatal  nonfatal  nonracial  mislabel  defrayal  portrayal  interracial  postnatal  interglacial  reappraisal  postnasal  craniofacial  metastable  multiracial  analysable  reimbursable