3 syllables:
oligist, ologist

4 syllables:
aerologist, agrologist, algologist, andrologist, apologist, astrologist, atmologist, battologist, biologist, bryologist, bugologist, carpologist, cetologist, chirologist, christologist, chronologist, conchologist, cosmologist, cryptologist, cytologist, dendrologist, ecologist, enologist, ethnologist, ethologist, fetologist, fungologist, garbologist, gastrologist, gemmologist, gemologist, geologist, glassologist, glottologist, graphologist, herbologist, hippologist, histologist, horologist, hydrologist, hymnologist, hypnologist, ichthyologist, indologist, limnologist, lithologist, mantologist, mazologist, metrologist, misologist, mixologist, moirologist, monologist, morphologist, mycologist, myologist, mythologist, necrologist, neologist, nephrologist, neurologist, nomologist, noologist, nosologist, oncologist, ontologist, oologist, orologist, otologist, pantologist, pathologist, patrologist, pedologist, penologist, petrologist, phenologist, philologist, phonologist, photologist, phrenologist, phycologist, phytologist, podologist, pomologist, psephologist, pseudologist, psychologist, psycologist, pyrologist, quinologist, rheologist, rhinologist, saintologist, scatologist, seismologist, serologist, sexologist, sinologist, spermologist, symbologist, tautologist, technologist, teuthologist, theologist, topologist, tribologist, trichologist, typologist, urologist, virologist, xenologist, zoologist, zymologist

5 syllables:
acarologist, aetiologist, agriologist, agrostologist, angiologist, anthropologist, apiologist, arachnologist, archaeologist, areologist, audiologist, axiologist, balneologist, bibliologist, bromatologist, campanologist, carcinologist, cardiologist, cereologist, chiroptologist, choreologist, climatologist, cosmetologist, craniologist, creatologist, criminologist, deltiologist, demonologist, deontologist, dermatologist, egyptologist, electrologist, embryologist, entomologist, enzymologist, erpetologist, escapologist, eschatologist, etiologist, etymologist, fermentologist, futurologist, galvanologist, genealogist, gerontologist, glaciologist, gynaecologist, gynecologist, haematologist, hagiologist, helminthologist, hematologist, hepatologist, heroologist, herpetologist, hierologist, iconologist, ideologist, immunologist, iridologist, kremlinologist, laryngologist, lexicologist, malacologist, mariologist, martyrologist, meterologist, methodologist, mineralogist, museologist, musicologist, myriologist, myrmecologist, nematologist, numerologist, oceanologist, odontologist, oenologist, oil geologist, ophiologist, ophthalmologist, opthalmologist, opthamologist, orchidologist, ornithologist, oryctologist, osteologist, paleologist, palynologist, pantheologist, papyrologist, pharmacologist, phraseologist, physiologist, planetologist, pneumatologist, primatologist, promorphologist, pteridologist, pulmonologist, radiologist, reflexologist, rheumatologist, roentgenologist, scientologist, selenologist, semiologist, sociologist, somatologist, spelaeologist, speleologist, stomatologist, synecologist, syphilologist, tegestologist, teratologist, terminologist, thanatologist, toxicologist, traumatologist, uranologist, urbanologist, vaccinologist, vermeologist, vexillologist, volcanologist, vulcanologist

6 syllables:
agrobiologist, assyriologist, astrobiologist, astrogeologist, bacteriologist, biotechnologist, chiropterologist, chronobiologist, conchyliologist, crustaceologist, cryobiologist, cryptozoologist, cytopathologist, cytotechnologist, dendrochronologist, diabetologist, dialectologist, dysteleologist, ecclesiologist, endocrinologist, entozoologist, epistemologist, exobiologist, geochronologist, geomorphologist, heresiologist, histopathologist, hydrobiologist, hydrogeologist, kinesiologist, liturgiologist, malariologist, meteorologist, microbiologist, nanotechnologist, neonatologist, neuro-oncologist, neurobiologist, neuropathologist, neuropsychologist, numismatologist, onomatologist, palaeontologist, palaetiologist, paleontologist, parapsychologist, parasitologist, perinatologist, phenomenologist, photobiologist, photogeologist, phytolithologist, phytopathologist, protozoologist, psychobiologist, psychopathologist, sovietologist, universologist, venereologist

7 syllables:
anaesthesiologist, anesthesiologist, clinical psychologist, ecotoxicologist, electro-biologist, epidemiologist, ethnomethodologist, ethnomusicologist, gastroenterologist, lepidopterologist, neuropharmacologist, neurophysiologist, neuroradiologist, otolaryngologist, paleobiologist, paleoecologist, paleopathologist, paleophytologist, paleozoologist, psychopharmacologist, psychophysiologist, radiobiologist, rhinolaryngologist, social anthropologist, sociobiologist

8 syllables:
electrophysiologist, hydrometeorologist, immunohematologist, micropaleontologist, neuroendocrinologist, palaeoanthropologist, palaeoclimatologist, paleoanthropologist, paleoclimatologist, petroleum geologist

9 syllables:
otorhinolaryngologist

3 syllables:
botanist, optimist, dramatist, competent, colonist, alchemist, dogmatist, occultist, bonavist, fossilist, sodomist, waffenschmidt

4 syllables:
copyedit, agronomist, monogamist, optometrist, romanticist, proctologist, economist, misogamist, anomalist, tobogganist

5 syllables:
anthropophagite