Legally binding owing to having been executed in compliance with the law; legally acceptable, in force, or valid.

Firmly or solidly established; of solid worth or value; of real significance, weighty; reliable… Of a statement, discourse, writing.

In full accordance with fact, reason, or good sense; founded on true or well-established grounds; free from error, fallacy, or logical defect…

Admissible, valid; worthy of consideration; able to be acknowledged.

Having legal force. Of a document: executed in compliance with the law, valid. Also figurative and in figurative contexts. Obsolete.

Not liable to fail or vary. Of a doctrine, theory, conclusion: Securely established, not likely to be disproved or found wanting.

Of things: Not liable to fail, unfailing. Not liable to prove false, erroneous, or mistaken; that unfailingly holds good.

Strong, weighty, valid. Obsolete.

Not falsified or perverted in any way. Of doctrine, etc.: Genuine, pure.

Recognized, confessed, owned; admitted as true, valid, or authoritative.

The quality of being well-founded on fact, or established on sound principles, and thoroughly… In the phrase of…validity.

Well-ascertained, certain, sure. Of an argument: Well-founded, valid. Obsolete.

Capable of being admitted or acknowledged (in various senses); recognizable.

Scottish. Valid, effective, decisive. Obsolete. rare.

That does not fail or prove false; = infallible, adj. 2.

In general use: Effective, effectual; sound.

Having the bottom covered or sheathed with copper. Also figurative thoroughly sound, genuine, authentic, trustworthy.