The Collaborative International Dictionary of English v.0.48:

Nil \Nil\ [See Nill, v. t.]
   Will not. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nil \Nil\, n. & a. [L., a contr. of nihil.]
   Nothing; of no account; worthless; -- a term often used for
   canceling, in accounts or bookkeeping. --A. J. Ellis.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nil \Nil\, n. (computers)
   A special value for a variable used in certain computer
   languages to mean no assigned value, to be distinguished from
   the value zero.
   [PJC]

WordNet (r) 3.0 (2006):

nil
    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]

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

NIL
 /nil/

    No. Used in reply to a question, particularly one asked using the ?-P?
    convention. Most hackers assume this derives simply from LISP terminology
    for ?false? (see also T), but NIL as a negative reply was
    well-established among radio hams decades before the advent of LISP. The
    historical connection between early hackerdom and the ham radio world was
    strong enough that this may have been an influence.


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

NIL

   /nil/ 1. New Implementation of Lisp.  A language intended to
   be the successor of MacLisp.  A large Lisp, implemented
   mostly in VAX assembly language.  A forerunner of Common
   LISP.

   ["NIL: A Perspective", Jon L. White, MACSYMA Users' Conf Proc,
   1979].

   2. Network Implementation Language.  Strom & Yemini, TJWRC,
   IBM.  Implementation of complex networking protocols in a
   modular fashion.

   ["NIL: An Integrated Language and System for Distributed
   Programming", R. Strom et al, SIGPLAN Notices 18(6):73-82
   (June 1983)].

   3. Empty list or False.  In Lisp, the empty list (or "nil
   list") is used to represent the Boolean value False.  This
   is possible because Lisp is not typed.  True is represented
   by the special atom "t".

   4. Spoken in reply to a question, particularly one asked using
   the "-P" convention it means "No".  Most hackers assume this
   derives simply from LISP, but NIL meaning "no" was
   well-established among radio hams decades before LISP existed.
   The historical connection between early hackerdom and the ham
   radio world was strong enough that this may have been an
   influence.

   [Jargon File]