Not counterfeit, spurious, false, or adulterated
Belonging to, or proceeding from the original stock; native
Genuine - as distinguished from efficient or regular - sacrament.
Well grounded or justifiable, pertinent.
Of an argument: whose conclusion is always true whenever its premises are true.
Related to the current topic, or presented within context, relevant.
Of a formula or system: such that it evaluates to true regardless of the input values.
Acceptable, proper or correct; in accordance with the rules.