3 syllables:
flectional, flexional

4 syllables:
adjectional, affectional, collectional, complexional, connectional, connexional, convectional, correctional, directional, evectional, inflectional, inflexional, inspectional, objectional, perfectional, projectional, protectional, reflectional

5 syllables:
bi-directional, bidirectional, insurrectional, interjectional, intersectional, introspectional, nondirectional, noninflectional, resurrectional, vivisectional

6 syllables:
multidirectional, omnidirectional, uni-directional, unidirectional

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, 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, congressional, electable, dispensable, preventable, unquenchable, processional, injectable, digestible, adjectival, atenolol, professional, illegible, heliacal, confessional, comestible, inflexible, delectable, insensible, ascendable, defensible, trigeminal, regrettable, contemptible, defendable, extendable, untenable, amendable, centesimal, accessible, commendable, amenable, intestinal, respectable, collectible, lamentable, expendable, correctable, perceptible, receptacle, contestable, execrable, recessional, polemical, incredible, conceptional, dependable, detestable, congenital, ostensible, preferable, impeccable, forgettable, collectable, compressible, susceptible, obsessional, conventional, intentional, inedible, exceptional, extensible, alchemical, church festival, discretional, jazz festival, raw vegetable, redemptional, resplendent quetzel, root vegetable, stand sentinel, unbendable, unrentable, untellable

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

6 syllables:
semiprofessional, heterosexual, recurring decimal, repeating decimal, multidimensional, unidimensional, paraprofessional, religious festival

7 syllables:
circulating decimal, electric receptacle