The Collaborative International Dictionary of English v.0.48:

Legal \Le"gal\ (l[=e]"gal), a. [L. legalis, fr. lex, legis, law;
   prob. orig., that which lies or is fixed (cf. L. lectus bed),
   and if so akin to E. lie, law: cf. F. l['e]gal. Cf. Lie to
   be prostrate, Loyal, Leal.]
   1. Created by, permitted by, in conformity with, or relating
      to, law; as, a legal obligation; a legal standard or test;
      a legal procedure; a legal claim; a legal trade; anything
      is legal which the laws do not forbid.
      [1913 Webster]

   2. (Theol.)
      (a) According to the law of works, as distinguished from
          free grace; or resting on works for salvation.
      (b) According to the old or Mosaic dispensation; in
          accordance with the law of Moses.
          [1913 Webster]

   3. (Law) Governed by the rules of law as distinguished from
      the rules of equity; as, legal estate; legal assets.
      --Bouvier. --Burrill.
      [1913 Webster]

   Legal cap. See under Cap.

   Legal tender.
      (a) The act of tendering in the performance of a contract
          or satisfaction of a claim that which the law
          prescribes or permits, and at such time and place as
          the law prescribes or permits.
      (b) That currency, or money, which the law authorizes a
          debtor to tender and requires a creditor to receive.
          It differs in different countries.

   Syn: Lawful; constitutional; legitimate; licit; authorized.
        See Lawful.
        [1913 Webster]

WordNet (r) 3.0 (2006):

legal
    adj 1: established by or founded upon law or official or
           accepted rules [ant: illegal]
    2: of or relating to jurisprudence; "legal loophole"
    3: having legal efficacy or force; "a sound title to the
       property" [syn: legal, sound, effectual]
    4: relating to or characteristic of the profession of law; "the
       legal profession"
    5: allowed by official rules; "a legal pass receiver"

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

legal

   Loosely used to mean "in accordance with all the relevant
   rules", especially in connection with some set of constraints
   defined by software.  "The older =+ alternate for += is no
   longer legal syntax in ANSI C."  "This parser processes each
   line of legal input the moment it sees the trailing linefeed."
   Hackers often model their work as a sort of game played with
   the environment in which the objective is to maneuver through
   the thicket of "natural laws" to achieve a desired objective.
   Their use of "legal" is flavoured as much by this game-playing
   sense as by the more conventional one having to do with courts
   and lawyers.  Compare language lawyer, legalese.

   [Jargon File]


The Jargon File (version 4.4.7, 29 Dec 2003):

legal
 adj.

    Loosely used to mean ‘in accordance with all the relevant rules’, esp. in
    connection with some set of constraints defined by software. “The older =+
    alternate for += is no longer legal syntax in ANSI C.” “This parser
    processes each line of legal input the moment it sees the trailing
    linefeed.” Hackers often model their work as a sort of game played with the
    environment in which the objective is to maneuver through the thicket of
    ‘natural laws’ to achieve a desired objective. Their use of legal is
    flavored as much by this game-playing sense as by the more conventional one
    having to do with courts and lawyers. Compare language lawyer, legalese
    .