valid

adj. legitimate, legally acceptable, not expired; based; logical, well-founded

The term validity as it occurs in logic refers generally to a property of deductive arguments, although many logic texts apply the term to statements as well (a statement is a sentence that “has a truth value,” i.e., that is either true or false). For the purposes of this article, an argument is a set of statements, one of which is the conclusion and the rest of which are premises. The premises are reasons intended to show that the conclusion is, or is probably, true.
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Adjective
1. well grounded in logic or truth or having legal force; "a valid inference"; "a valid argument"; "a valid contract"; "a valid license"
(antonym) invalid
(similar) binding
(see-also) legitimate
2. still legally acceptable; "the license is still valid"
(similar) unexpired

adj. valid, legitimate, binding

(a.)
Strong; powerful; efficient.
  

(a.)
Having sufficient strength or force; founded in truth; capable of being justified, defended, or supported; not weak or defective; sound; good; efficacious; as, a valid argument; a valid objection.
  

(a.)
Having legal strength or force; executed with the proper formalities; incapable of being rightfully overthrown or set aside; as, a valid deed; a valid covenant; a valid instrument of any kind; a valid claim or title; a valid marriage.