Here's what rhymes with undefendedness.
                        
                        
                    
                                Words that almost rhyme with undefendedness
fetidness  venomous  senselessness  defencelessness  defenselessness  fecklessness  eventfulness  sensibleness  tepidness  genesis  stenosis  carelessness  gentleness  helplessness  sensuous  tenuous  tetanus  blessedness  recklessness  helpfulness  carefulness  fretfulness  healthfulness  sedulous  infectiousness  tendentiousness  levelness  mechanise  resentfulness  zestfulness  heftiness  resonance  feminists  perilous  sediments  decadence  mellitus  membranous  restlessness  licentiousness  nebulous  preparedness  garrulous  pendulous  breathlessness  emeritus  baronets  preciousness  pretentiousness  unpreparedness  relentlessness  restfulness  dreadfulness  impetuousness  terribleness  testiness  redolence  nonvenomous  djellabas  incestuousness  marabous  jellabas  inheritance  sentiments  negligence  relevance  precedence  forgetfulness  pathogenesis  precipice  tenements  asparagus  credulous  preeminence  requisites  unpleasantness  angiogenesis  irrelevance  pleasantness  querulous  clarinets  petulance  contentiousness  decadents  directionless  megabits  perfectionists  momentousness  respectfulness  decimates  portentousness  tempestuousness  dextrousness  developments  intelligence  settlements  prevalence  regiments  specialists  benevolence  precedents  impediments  pestilence  beneficence  incredulous  tremulous  conscientiousness  morphogenesis  overemphasis  celebrants  interrogates  presentiments  detriments  secondments  housemistress  neglectfulness  experiments  hydrocephalus  prerequisites  temperaments  embryogenesis  geneticists  malevolence  integuments  nonresidents  registrants  testaments  disinheritance  embarrassments  spermatogenesis  nonspecialists  contemptuousness  redevelopments  gluconeogenesis