Here's what rhymes with mainsail.
                        
                        
                    
                                fail  sale  sail  veil  hail  shale  vale  hale  faille  male  scale  mail  pale  tail  tale  avail  jail  nail  rail  frail  gale  whale  bail  stale  wail  assail  bale  dale  inhale  pail  snail  flail  kale  unveil  wale  trail  entail  email  quail  quale  braille  grail  impale  monorail  wassail  hightail  detail  prevail  travail  curtail  exhale  bewail  derail  gunwale  topsail  foresail  taffrail  lugsail  carrell  pigtail  ponytail  countervail  bobtail  nonpareil  pellmell  hangnail  fingernail  martingale  swallowtail  tattletale