18 letters
- phytohemagglutinin38
- piezoelectricities37
- polyacrylonitriles32
- polychromatophilia38
- polychromatophilic41
- polyesterification31
- polyribonucleotide34
- postmillenarianism31
- postmillennialisms32
- postmillennialists29
- postpsychoanalytic38
- praiseworthinesses27
- predestinarianisms27
- premillenarianisms31
- proletarianization33
- pronounceabilities31
- propagandistically35
- provincializations40
- pseudotuberculosis32
- psychoanalytically39
- psychobiographical42
- psychopathological40
- psychopathologists36
- psychophysiologies38
- psychophysiologist38
- quantificationally40
- quantitativenesses34
- quasiperiodicities35
- quattuordecillions36
- questionablenesses34
- radiochromatograms32
- radiosensitivities24
- rambunctiousnesses31
- rechromatographies33
- rechromatographing36
- reconstructionisms30
- reconstructionists27
- recrystallizations35
- redistributionists24
- rehospitalizations34
- reinstitutionalize31
- remunerativenesses28
- renationalizations31
- reprehensibilities28
- representationally27
- representativeness27
- representativities26
- revascularizations37
- ribonucleoproteins31
- roentgenologically32
- sacrilegiousnesses26
- satisfactorinesses25
- sedimentologically33
- semiconservatively36
- semidomestications29
- semipermeabilities31
- semiprofessionally32
- semiquantitatively39
- sentimentalization34
- shortsightednesses26
- simplemindednesses32
- simultaneousnesses26
- sociopsychological38
- somnambulistically37
- soporiferousnesses26
- spectrofluorimeter32
- spectrographically38
- spectroheliographs34
- spectroheliography36
- spectrohelioscopes33
- spectrophotometric35
- sphygmomanometries37
- stereophotographic33
- stereoregularities22
- stereospecifically34
- stoichiometrically33
- structuralizations34
- subcategorizations37
- subclassifications33
- subconsciousnesses31
- submicroscopically41
- substitutabilities27
- superadministrator27
- superciliousnesses28
- supercivilizations40
- superintellectuals30
- superintelligences31
- superminicomputers36
- supersensitivities27
- supersophisticated31
- supranationalities25
- tachistoscopically36
- telecommunications34
- territorialization29
- theatricalizations34
- thermoluminescence36
- thermoplasticities30
- thrombophlebitides36
- transcendentalisms29
- transcendentalists26
- transformationally30
- transilluminations27
- transistorizations29
- transmissibilities26
- transmogrification31
- transportabilities26
- transubstantiating27
- transubstantiation25
- triboelectricities28
- triboluminescences34
- trichloroethylenes30
- triskaidekaphobias35
- ultracentrifugally34
- ultraconservatisms31
- ultraconservatives32
- ultramicroscopical36
- ultranationalistic26
- ultrarevolutionary29
- ultrasophisticated29
- unaccountabilities32
- unassailablenesses26
- unattractivenesses28
- uncharitablenesses30
- uncompromisingness36
- unconscionableness33
- unconstitutionally30
- unconvincingnesses36
- unenthusiastically31
- ungrammaticalities32
- uniformitarianisms30
- unintelligibleness30
- unpredictabilities31
- unprinciplednesses33
- unprofitablenesses31
- unresponsivenesses29
- unrestrainednesses23
- unsatisfactoriness27
- unsubstantialities26
- vaingloriousnesses28
- valetudinarianisms30
- verisimilitudinous30
- videoconferencings37