The Collaborative International Dictionary of English v.0.48:

hacker \hack"er\ (h[a^]k"[~e]r), n.
   One who, or that which, hacks. Specifically: A cutting
   instrument for making notches; esp., one used for notching
   pine trees in collecting turpentine; a hack.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hacker
    n 1: someone who plays golf poorly
    2: a programmer who breaks into computer systems in order to
       steal or change or destroy information as a form of cyber-
       terrorism [syn: hacker, cyber-terrorist, cyberpunk]
    3: a programmer for whom computing is its own reward; may enjoy
       the challenge of breaking into other computers but does no
       harm; "true hackers subscribe to a code of ethics and look
       down upon crackers"
    4: one who works hard at boring tasks [syn: hack, drudge,
       hacker]

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

hacker
 n.

    [originally, someone who makes furniture with an axe]

    1. A person who enjoys exploring the details of programmable systems and
    how to stretch their capabilities, as opposed to most users, who prefer to
    learn only the minimum necessary. RFC1392, the Internet Users' Glossary,
    usefully amplifies this as: A person who delights in having an intimate
    understanding of the internal workings of a system, computers and computer
    networks in particular.

    2. One who programs enthusiastically (even obsessively) or who enjoys
    programming rather than just theorizing about programming.

    3. A person capable of appreciating hack value.

    4. A person who is good at programming quickly.

    5. An expert at a particular program, or one who frequently does work using
    it or on it; as in ?a Unix hacker?. (Definitions 1 through 5 are
    correlated, and people who fit them congregate.)

    6. An expert or enthusiast of any kind. One might be an astronomy hacker,
    for example.

    7. One who enjoys the intellectual challenge of creatively overcoming or
    circumventing limitations.

    8. [deprecated] A malicious meddler who tries to discover sensitive
    information by poking around. Hence password hacker, network hacker. The
    correct term for this sense is cracker.

    The term ?hacker? also tends to connote membership in the global community
    defined by the net (see the network. For discussion of some of the basics
    of this culture, see the How To Become A Hacker FAQ. It also implies that
    the person described is seen to subscribe to some version of the hacker
    ethic (see hacker ethic).

    It is better to be described as a hacker by others than to describe oneself
    that way. Hackers consider themselves something of an elite (a meritocracy
    based on ability), though one to which new members are gladly welcome.
    There is thus a certain ego satisfaction to be had in identifying yourself
    as a hacker (but if you claim to be one and are not, you'll quickly be
    labeled bogus). See also geek, wannabee.

    This term seems to have been first adopted as a badge in the 1960s by the
    hacker culture surrounding TMRC and the MIT AI Lab. We have a report that
    it was used in a sense close to this entry's by teenage radio hams and
    electronics tinkerers in the mid-1950s.


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

hacker

    (Originally, someone who makes furniture with
   an axe) 1. A person who enjoys exploring the details of
   programmable systems and how to stretch their capabilities, as
   opposed to most users, who prefer to learn only the minimum
   necessary.

   2. One who programs enthusiastically (even obsessively) or who
   enjoys programming rather than just theorizing about
   programming.

   3. A person capable of appreciating hack value.

   4. A person who is good at programming quickly.

   5. An expert at a particular program, or one who frequently
   does work using it or on it; as in "a Unix hacker".
   (Definitions 1 through 5 are correlated, and people who fit
   them congregate.)

   6. An expert or enthusiast of any kind.  One might be an
   astronomy hacker, for example.

   7. One who enjoys the intellectual challenge of creatively
   overcoming or circumventing limitations.

   8. (Deprecated) A malicious meddler who tries to discover
   sensitive information by poking around.  Hence "password
   hacker", "network hacker".  The correct term is cracker.

   The term "hacker" also tends to connote membership in the
   global community defined by the net (see The Network and
   Internet address).  It also implies that the person
   described is seen to subscribe to some version of the hacker
   ethic.

   It is better to be described as a hacker by others than to
   describe oneself that way.  Hackers consider themselves
   something of an elite (a meritocracy based on ability), though
   one to which new members are gladly welcome.  Thus while it is
   gratifying to be called a hacker, false claimants to the title
   are quickly labelled as "bogus" or a "wannabee".

   9. (University of Maryland, rare) A programmer who does not
   understand proper programming techniques and principles and
   doesn't have a Computer Science degree.  Someone who just
   bangs on the keyboard until something happens.  For example,
   "This program is nothing but spaghetti code.  It must have
   been written by a hacker".

   [Jargon File]

   (1996-08-26)