The Collaborative International Dictionary of English v.0.48:

User \Us"er\, n.
   1. One who uses. --Shak.
      [1913 Webster]

   2. (Law) Enjoyment of property; use. --Mozley & W.
      [1913 Webster]

WordNet (r) 3.0 (2006):

user
    n 1: a person who makes use of a thing; someone who uses or
         employs something
    2: a person who uses something or someone selfishly or
       unethically [syn: exploiter, user]
    3: a person who takes drugs [syn: drug user, substance
       abuser, user]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "user":
   LSD user, acidhead, addict, alcoholic, buyer, chain smoker,
   cocaine sniffer, cokie, consumer, cubehead, dipsomaniac,
   dope fiend, doper, droit du seigneur, drug abuser, drug addict,
   drug user, drunkard, employer, enjoyer, enjoyment of property,
   fiend, freak, glue sniffer, habitual, head, heavy smoker, hophead,
   hype, imperfect usufruct, junkie, marijuana smoker, methhead,
   narcotics addict, operator, owner, perfect usufruct, pillhead,
   pothead, purchaser, right of use, snowbird, speed freak, tripper,
   usufruct



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

user
 n.

    1. Someone doing ?real work? with the computer, using it as a means rather
    than an end. Someone who pays to use a computer. See real user.

    2. A programmer who will believe anything you tell him. One who asks silly
    questions. [GLS observes: This is slightly unfair. It is true that users
    ask questions (of necessity). Sometimes they are thoughtful or deep. Very
    often they are annoying or downright stupid, apparently because the user
    failed to think for two seconds or look in the documentation before
    bothering the maintainer.] See luser.

    3. Someone who uses a program from the outside, however skillfully, without
    getting into the internals of the program. One who reports bugs instead of
    just going ahead and fixing them.

    The general theory behind this term is that there are two classes of people
    who work with a program: there are implementors (hackers) and lusers. The
    users are looked down on by hackers to some extent because they don't
    understand the full ramifications of the system in all its glory. (The few
    users who do are known as real winners.) The term is a relative one: a
    skilled hacker may be a user with respect to some program he himself does
    not hack. A LISP hacker might be one who maintains LISP or one who uses
    LISP (but with the skill of a hacker). A LISP user is one who uses LISP,
    whether skillfully or not. Thus there is some overlap between the two
    terms; the subtle distinctions must be resolved by context.


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

user

   1.  Someone doing "real work" with the computer, using
   it as a means rather than an end.  Someone who pays to use a
   computer.  A programmer who will believe anything you tell
   him.  One who asks silly questions without thinking for two
   seconds or looking in the documentation.  Someone who uses a
   program, however skillfully, without getting into the
   internals of the program.  One who reports bugs instead of
   just fixing them.  See also luser, real user.

   Users are looked down on by hackers to some extent because
   they don't understand the full ramifications of the system in
   all its glory.  The term is relative: a skilled hacker may be
   a user with respect to some program he himself does not hack.
   A LISP hacker might be one who maintains LISP or one who uses
   LISP (but with the skill of a hacker).  A LISP user is one who
   uses LISP, whether skillfully or not.  Thus there is some
   overlap between the two terms; the subtle distinctions must be
   resolved by context.

   2.  Any person, organisation, process, device,
   program, protocol, or system which uses a service provided
   by others.

   The term "client" (as in "client-server" systems) is
   rather more specific, usually implying two processes
   communicating via some protocol.

   [Jargon File]

   (1996-04-28)