3 syllables:
sessional

4 syllables:
accessional, compressional, confessional, congressional, digressional, discretional, expressional, impressional, obsessional, possessional, precessional, processional, professional, progressional, recessional, secessional, successional, transgressional

5 syllables:
health professional, intercessional, non-professional, nonprofessional, preprofessional, subprofessional, unprofessional

6 syllables:
extraprofessional, paraprofessional, semi-professional, semiprofessional

3 syllables:
tenable, equable, estival, medical, stretchable, sensual, skeletal, sextuple, pessimal, sensible, edible, meltable, vegetable, vendible, retinal, festival, aestival, flexible, spectacle, sentinel, pedestal, sepulchral, bendable, legible, credible, methanal, peccable, epochal, plentiful, sectional, seconal, decimal, vegetal, seneschal, genital, skeptical, ethical, gettable, tentacle, testable, jezebel, seminal, rentable, pennoncel, requital, spendable, chemical, pentacle, denticle, edental, emmental, epical, getable, kettleful, reticle, sceptical, sellable, vendable

4 syllables:
impregnable, acceptable, ineffable, conventicle, dimensional, condemnable, detectable, expressible, compensable, inflectional, electable, dispensable, preventable, unquenchable, injectable, digestible, adjectival, atenolol, illegible, heliacal, comestible, inflexible, delectable, insensible, ascendable, defensible, trigeminal, regrettable, contemptible, defendable, correctional, extendable, untenable, amendable, centesimal, accessible, commendable, amenable, intestinal, respectable, affectional, collectible, lamentable, expendable, directional, correctable, perceptible, receptacle, contestable, execrable, polemical, incredible, conceptional, dependable, detestable, congenital, ostensible, preferable, impeccable, forgettable, collectable, compressible, susceptible, conventional, intentional, inedible, exceptional, extensible, alchemical, church festival, jazz festival, raw vegetable, redemptional, resplendent quetzel, root vegetable, stand sentinel, unbendable, unrentable, untellable

5 syllables:
hexadecimal, unexceptional, incompressible, apprehensible, comprehensible, inextensible, bidirectional, inaccessible, undependable, three-dimensional, neurochemical, indispensable, unconventional, two-dimensional, unintentional, indigestible, hypothetical, inexpressible, reprehensible, irrepressible, pyrotechnical, insurrectional, indefensible, planetesimal, unforgettable, insusceptible, unacceptable, homosexual, catechetical, commonsensible, incontestable, incontestible, leafy vegetable, one-dimensional, third-dimensional, unaccessible, unamenable, uncorrectable, undefendable, undetectable, unexpendable, unexpressible, uninjectable, unpresentable, unpreventable, unrespectable, unsusceptible

6 syllables:
omnidirectional, heterosexual, recurring decimal, unidirectional, repeating decimal, multidimensional, unidimensional, religious festival

7 syllables:
circulating decimal, electric receptacle