inferential — of, pertaining to, by, or dependent upon inference.
influential — having or exerting influence, especially great influence: three influential educators.
nonessential — not essential; not necessary: Nonessential use of gasoline was forbidden during the war.
preferential — of, relating to, or of the nature of preference: preferential policies.
presidential — of or relating to a president or presidency.
providential — of, relating to, or resulting from divine providence: providential care.
quintessential — of the pure and essential essence of something: the quintessential Jewish delicatessen.
residential — of or relating to residence or to residences: a residential requirement for a doctorate.
reverential — of the nature of or characterized by reverence; reverent: reverential awe.
Four-or-more syllable rhymes
action potential — a localized change in electrical potential, from about –70 mV to +30 mV and back again, that occurs across a nerve fibre during transmission of a nerve impulse
experiential — Involving or based on experience and observation.
inconsequential — of little or no importance; insignificant; trivial.