(a.) Adequate; sufficient to produce a desired effect; as, an effectual writing method\; efficient; operative; decisive.

able achieving active actual adequate ascertained attested authenticated authoritative banausic behind the scenes binding capable categorically true causal causative certain certified charismatic charming competent conclusive confirmed consequential constitutive corroborated decisive demonstrated determinative determined documentary effective efficacious efficient enchanting equal to established estimable etiological factual feasible forceful forcible formative fulfilling functional go historical important in force influential institutive lawful legal magnetic momentous not in error objectively true occasional operable operational operative originative personable persuasive pivotal potent powerful practicable practical pragmatic prestigious productive proficient proved real realizable reputable sound strong suasive substantial substantiated sure-enough telling toothy TRUE true as gospel truthful unconfuted undenied undoubted unerroneous unfallacious unfalse unmistaken unquestionable unrefuted up to useful valid validated veracious verified veritable weighty winning workable