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

4 syllables:
dirigible, heritable, charitable, perinatal, irritable, corrigible, acceptable, accessible, affectional, alchemical, amenable, amendable, ascendable, church festival, collectable, collectible, commendable, compensable, compressible, conceptional, confessional, congenital, congressional, contemptible, contestable, conventional, correctable, correctional, defendable, defensible, delectable, dependable, detectable, detestable, digestible, dimensional, directional, discretional, dispensable, electable, exceptional, execrable, expendable, expressible, extendable, extensible, forgettable, illegible, impeccable, impregnable, incredible, inedible, ineffable, inflectional, inflexible, injectable, insensible, intentional, intestinal, jazz festival, lamentable, obsessional, ostensible, perceptible, polemical, preventable, processional, professional, raw vegetable, receptacle, recessional, redemptional, regrettable, respectable, resplendent quetzel, root vegetable, stand sentinel, susceptible, trigeminal, unbendable, unquenchable, unrentable, untellable, untenable

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

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

7 syllables:
circulating decimal, electric receptacle