15 letters

perchloroethene ∙ percussophilist perdurabilities ∙ perfectibilians ∙ perfectibilisms ∙ perfectibilists ∙ perfectionating ∙ perfectionation perfectionistic ∙ perfervidnesses ∙ perfluorocarbon ∙ perfunctoriness ∙ pergamentaceous ∙ perhydrogenized periadventitial periamygdalitis Periappendiceal peribronchiolar pericanalicular pericardiectomy pericardiolysis pericardiostomy pericholangitis peridentoclasia periesophagitis perigastritises ∙ periglandulitis perihepatitises ∙ periligamentous perilymphangial perimyocarditis perinephritises ∙ periodontically ∙ periodontitises ∙ periodontolysis perioesophageal periostosteitis peripatetically ∙ peripateticisms ∙ peripheralities ∙ peripheroceptor peripheromittor peripheroneural periprostatitis perirhizoclasia perisalpingitis periselectivity perishabilities ∙ perisigmoiditis perispermatitis perisphinctidae perispondylitis perisporiaceous perissodactyles ∙ perissodactylic ∙ perissosyllabic ∙ peristaltically ∙ peristaphylitis peristerophobia peristeropodous perithyroiditis peritonealizing peritoneoclysis peritoneoplasty peritoneovenous peritonsillitis perityphlitises ∙ perivesiculitis permanentnesses ∙ permeablenesses ∙ permissibleness ∙ permutabilities ∙ permutationists peronosporaceae peroratorically peroxysulphuric ∙ perpendicularly ∙ perplexednesses ∙ persecutiveness persnicketiness ∙ Personalisation ∙ personalization ∙ personification ∙ personificative perspectiveless perspectography perspicaciously ∙ perspicuousness ∙ persuadableness persuasibleness persulphocyanic pervasivenesses ∙ pervertednesses ∙

16 letters

perchlorethylene perchloromethane Perfluorocarbons perforationproof perfunctoriously perhydrogenation perhydrogenizing periappendicitis periappendicular periconceptional peridromophilist periencephalitis perifolliculitis perigastrulation perilymphangitis perineosynthesis periodontoclasia periodontologist periophthalmitis periosteorrhaphy peripancreatitis peripericarditis peripherocentral periphrastically perisplanchnitis perissodactylate perissodactylism perissodactylous peristeromorphae peristeromorphic peristerophilist perithyreoiditis peritrochanteric perjurymongering permonosulphuric peroneocalcaneal peronosporaceous Perpendicularity perpilocutionist personifications persulphocyanate pertinaciousness pervicaciousness

17 letters

perchloroethylene perennibranchiata perennibranchiate perfectionizement periangiocholitis peribronchiolitis pericardicentesis pericardiophrenic pericardiopleural pericardiorrhaphy pericementoclasia pericholecystitis perilabyrinthitis periosteoalveolar periosteomyelitis peripylephlebitis peristeromorphous peritoneocentesis peritoneomuscular permineralization perpendicularness Personalapplicant perspicaciousness

18 letters

percrystallization perfectibilitarian perhydroanthracene pericardiocentesis peridiverticulitis permocarboniferous

19 letters

pericardiacophrenic pericardiosymphysis periosteomedullitis peripachymeningitis peroxidicperoxiding

20 letters

pericardioperitoneal perisalpingoovaritis peritoneopericardial

22 letters

perioophorosalpingitis PersonalRepresentative

23 letters

pericardiomediastinitis

Words with a ∙ are valid Scrabble words (SOWPODS word list)