You can make more than 25,000 words. Here are some of the bigger words:

14-letter words

administration, administrators, aerodynamicist, aminoacidurias, amitriptylines, anisometropias, anticapitalism, anticorruption, antimodernists, antimonopolist, antineoplastic, antiradicalism, antiritualisms, antiterrorisms, apostolicities, autoeroticisms, compassionated, compensational, conditionality, considerations, consolidations, conspirational, conspiratorial, consuetudinary, containerports, contemplations, contemporarily, contemptuously, conterminously, contraposition, cooperationist, corruptionists, counterassault, decompositions, decontaminator, demolitionists, demonstrations, denticulations, dimensionality, directionality, disarticulates, discolorations, disconsolation, discourteously, discriminators, discriminatory, disorientation, dispensational, disputatiously, dissertational, doctrinairisms, documentalists, documentarians, documentarists, documentations, domestications, dramatisations, educationalist, emotionalistic, encapsulations, endoparasitism, impersonations, inauspiciously, incorporations, indoctrinators, insurrectional, intercalations, interpolations, interpositions, intracutaneous, introductorily, introspections, irrationalisms, irrationalists, latitudinarian, macronutrients, mariculturists, matriculations, micronutrients, micropulsation, misarticulated, misarticulates, miscorrelation, misdescription, misorientation, mistranslation, modernisations, monotonicities, monounsaturate, multiprocessor, neuroanatomist, noncapitalists, noncompetitors, nortriptylines, operationalism, operationalist, osteosarcomata, outmanipulated, outmanipulates, paediatricians, pararosaniline, parsimoniously, particularised, particularises, particularisms, particularists, pertinaciously, platinocyanide, pneumoconiosis, polymerisation, postindustrial, predominations, preordinations, procrastinated, procrastinates, procrastinator, protectionisms, radiostrontium, ratiocinations, reactionaryism, recapitulation, recompilations, recompositions, recomputations, recriminations, reduplications, reimplantation, reimportations, reinoculations, reintroduction, remonstrations, repristination, repudiationist, repunctuations, restimulations, restrictionism, retranslations, sacramentalist, solitudinarian, specialisation, supercriminals, superinduction, supernormality, supernutrition, territorialism, traditionalism, transcriptions, transcutaneous, transductional, translocations, transpirations, triamcinolones, tridimensional, ultradistances, ultraminiature, ultramodernist, ultraprecision, uncontemporary, unidirectional, unincorporated

15-letter words

administrations, aerodynamicists, anticapitalisms, anticorruptions, antieducational, antimonopolists, antiradicalisms, antirationalism, antispeculation, autocorrelation, cardiopulmonary, compassionately, connaturalities, contrapositions, cooperationists, decontaminators, demonstrational, dictatorialness, disarticulation, discontinuously, disorientations, documentational, educationalists, emancipationist, insurrectionary, insurrectionist, intercomparison, intermodulation, introspectional, latitudinarians, malpractitioner, microporosities, micropulsations, microtonalities, miscorrelations, misorientations, monounsaturated, monounsaturates, neuroanatomical, neuroanatomists, nonmatriculated, omnidirectional, operationalisms, operationalists, paranormalities, pararosanilines, particularities, platinocyanides, platitudinarian, polymerisations, polyunsaturated, postinoculation, postirradiation, procrastination, procrastinators, radioprotection, radiostrontiums, reactionaryisms, recapitulations, reimplantations, reincorporation, reintroductions, repristinations, repudiationists, sanctimoniously, solitudinarians, superinductions, supernaturalism, supernaturalist, supernutritions, supersaturation, surreptitiously, territorialisms, traditionalisms, transcriptional, transpirational, transpositional, ultramodernists, ultraprecisions, unanticipatedly, uncompassionate, unparliamentary

16-letter words

administratrices, antirationalisms, antireductionism, antispeculations, autocorrelations, coadministration, disarticulations, emancipationists, interassociation, intercomparisons, intermodulations, intracutaneously, introspectionism, malpractitioners, mistranscription, nonmaterialistic, operationalistic, platitudinarians, procrastinations, radioprotections, reincorporations, supranationalism, supranationalist, supranationality

17-letter words

antireductionisms, coadministrations, supernaturalistic, transdisciplinary, ultracontemporary

18-letter words

superadministrator, supranationalities