The Collaborative International Dictionary of English v.0.48:

Valid \Val"id\, a. [F. valide, L. validus strong, from valere to
   be strong. See Valiant.]
   [1913 Webster]
   1. Strong; powerful; efficient. [Obs.] "Perhaps more valid
      arms . . . may serve to better us." --Milton.
      [1913 Webster]

   2. 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.
      [1913 Webster]

            An answer that is open to no valid exception. --I.
                                                  Taylor.
      [1913 Webster]

   3. (Law) 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.
      [1913 Webster]

   Syn: Prevalent; available; efficacious; just; good; weighty;
        sufficient; sound; well-grounded.
        [1913 Webster]

WordNet (r) 3.0 (2006):

valid
    adj 1: well grounded in logic or truth or having legal force; "a
           valid inference"; "a valid argument"; "a valid contract"
           [ant: invalid]
    2: still legally acceptable; "the license is still valid"

Moby Thesaurus II by Grady Ward, 1.0:

153 Moby Thesaurus words for "valid":
   absolute, acceptable, actionable, adducible, admissible,
   advantageous, applicable, armipotent, attestative, attested,
   attestive, auspicious, authentic, authoritative, authorized,
   based on, beneficial, benevolent, binding, bon, bonny, braw, bueno,
   capital, certain, circumstantial, cogent, commendable, competent,
   conclusive, confirmed, consistent, constitutional, convincing,
   corroborated, cumulative, damning, decisive, definitive,
   demonstrated, determinative, determined, documentary, documented,
   dynamic, effective, effectual, elegant, energetic, established,
   estimable, evidential, evidentiary, ex parte, excellent, expedient,
   eye-witness, factual, fair, famous, favorable, final, fine,
   firsthand, forceful, forcible, founded on, good, goodly, grand,
   grounded on, healthy, hearsay, helpful, high-potency, high-powered,
   high-pressure, high-tension, implicit, in force, in power,
   incontrovertible, indicative, indisputable, irrefutable,
   irresistible, judicial, juridical, just, justiciable, kind, kosher,
   laudable, lawful, lawmaking, legal, legislative, legit, legitimate,
   licit, logical, material, mighty, mighty in battle, nice, noble,
   nuncupative, operative, overwhelming, persuasive, pleasant, potent,
   powerful, prepotent, presumptive, probative, profitable, puissant,
   regal, reliable, rightful, royal, ruling, sanctioned, satisfactory,
   satisfying, self-consistent, significant, skillful, solid, sound,
   splendid, statutory, striking, strong, substantial, substantiated,
   sufficient, suggestive, sure, symptomatic, telling, useful,
   validated, verified, very good, vigorous, virtuous, vital, weighty,
   well-founded, well-grounded, within the law



The Free On-line Dictionary of Computing (30 December 2018):

Valid

   A dataflow language.

   ["A List-Processing-Oriented Data Flow Machine Architecture",
   Makoto Amamiya et al, AFIPS NCC, June 1982, pp. 143-151].

   (1995-02-14)


Bouvier's Law Dictionary, Revised 6th Ed (1856):

VALID. An act, deed, will, and the like, which has received all the
formalities required by law, is said to be valid or good in law.