3 syllables:
myologists

4 syllables:
apologists, astrologists, biologists, chronologists, cosmologists, cryptologists, cytologists, ecologists, ethnologists, ethologists, geologists, graphologists, histologists, horologists, hydrologists, ichthyologists, limnologists, mixologists, monologists, morphologists, mycologists, mythologists, necrologists, nephrologists, neurologists, oncologists, ontologists, otologists, pathologists, pedologists, penologists, philologists, phrenologists, phycologists, proctologists, psephologists, psychologists, scatologists, seismologists, serologists, sexologists, sinologists, tautologists, technologists, topologists, urologists, virologists, zoologists

5 syllables:
acarologists, anthropologists, archaeologists, archeologists, audiologists, campanologists, cardiologists, climatologists, cosmetologists, craniologists, creatologists, criminologists, demonologists, deontologists, dermatologists, embryologists, entomologists, escapologists, eschatologists, etymologists, futurologists, gerontologists, glaciologists, gynaecologists, gynecologists, haematologists, hematologists, herpetologists, ideologists, immunologists, kremlinologists, laryngologists, malacologists, mineralogists, musicologists, numerologists, odontologists, oenologists, ophthalmologists, ornithologists, osteologists, pharmacologists, physiologists, radiologists, reflexologists, rheumatologists, scientologists, semiologists, sociologists, speleologists, teratologists, toxicologists, vexillologists, volcanologists, vulcanologists

6 syllables:
bacteriologists, biotechnologists, cryobiologists, cryptozoologists, endocrinologist's, endocrinologists, epistemologists, kinesiologists, meteorologist's, meteorologists, microbiologists, neonatologists, neurobiologists, neuropsychologists, paleontologists, parapsychologists, parasitologists, phenomenologists, psychobiologists, psychopathologists, sovietologists, venereologists

7 syllables:
anaesthesiologists, anesthesiologists, epidemiologists, ethnomusicologists, gastroenterologists, otolaryngologists, psychopharmacologists, radiobiologists

9 syllables:
otorhinolaryngologists

3 syllables:
deaconess, reasonless, speciousness, preciousness, heedlessness, evenness, sleeplessness, treasonous, peacefulness, feebleness, competence, mons pubis, notropis, ononis, os pubis, politics, prosopis, solidus

4 syllables:
deceitfulness, ingeniousness, deviousness, acanthophis, apocalypse, economise, economists, ecphonesis, mirabilis, odontaspis, unconsciousness, with competence

5 syllables:
agreeableness, geopolitics, power politics

6 syllables:
disagreeableness