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"

The Free On-line Dictionary of Computing (19 January 2023):

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)