The Collaborative International Dictionary of English v.0.48:

Null \Null\, v. t. [From null, a., or perh. abbrev. from annul.]
   To annul. [Obs.] --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Null \Null\, n. [Etymol. uncertain.]
   One of the beads in nulled work.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Null \Null\, a. [L. nullus not any, none; ne not + ullus any, a
   dim. of unus one; cf. F. nul. See No, and One, and cf.
   None.]
   1. Of no legal or binding force or validity; of no efficacy;
      invalid; void; nugatory; useless.
      [1913 Webster]

            Faultily faultless, icily regular, splendidly null,
            Dead perfection; no more.             --Tennyson.
      [1913 Webster]

   2. Having a value of zero; as, of null utility.
      [PJC]

   3. (Math.) Empty; having no members; as, the null set.
      [PJC]

   4. (Computers) Unassigned or meaningless; -- a special value
      given to variables, especially pointers or logical
      variables, indicating that it is meaningless and cannot be
      used in computation; as, an uninitialized pointer in "C"
      is given a null value. The actual value that is stored in
      memory to indicate the null condition may vary with the
      computer language used.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Null \Null\, n.
   1. Something that has no force or meaning.
      [1913 Webster]

   2. That which has no value; a cipher; zero. --Bacon.
      [1913 Webster]

   Null method (Physics.), a zero method. See under Zero.
      [1913 Webster]

WordNet (r) 3.0 (2006):

null
    adj 1: lacking any legal or binding force; "null and void" [syn:
           null, void]
    n 1: a quantity of no importance; "it looked like nothing I had
         ever seen before"; "reduced to nil all the work we had
         done"; "we racked up a pathetic goose egg"; "it was all for
         naught"; "I didn't hear zilch about it" [syn: nothing,
         nil, nix, nada, null, aught, cipher, cypher,
         goose egg, naught, zero, zilch, zip, zippo]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "null":
   aimless, bad, bare, barren, bland, blank, bleached, characterless,
   clear, designless, devoid, empty, existless, featureless, garbled,
   hollow, importless, inane, ineffective, ineffectual, inefficacious,
   insignificant, insipid, invalid, lacking, meaningless, minus,
   missing, negative, nonconnotative, nondenotative, nonexistent,
   null and void, phatic, purportless, purposeless, scrambled,
   senseless, unexisting, unmeaning, unrelieved, unsignificant,
   useless, vacant, vacuous, void, white, with nothing inside,
   without being, without content, worthless



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

null

    A special value used in several languages to
   represent the thing referred to by an uninitialised pointer.

    A special value that may be stored in some database
   columns to represent an unknown, missing, not applicable, or
   undefined value.  Nulls are treated completely differently
   from ordinary values when evaluating SQL expressions and there
   are several SQL constructs for dealing with nulls.

   (2003-06-17)


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

NULL. Properly, that which does not exist; that which is not in the nature
of things. In a figurative sense it signifies that which has no more effect
than if it did not exist. 8 Toull. n. 320.