The Collaborative International Dictionary of English v.0.48:

yahoo \ya"hoo\ (y[aum]"h[=oo]), n.
   1. One of a race of filthy brutes resembling men but subject
      to the Houyhnhnms in Swift's "Gulliver's Travels." See in
      the Dictionary of Noted Names in Fiction.
      [Webster 1913 Suppl. + WordNet 1.5 + CM]

   2. Hence, any brutish or vicious character.
      [Webster 1913 Suppl.]

   3. A raw countryman; a lout; a greenhorn. [U. S.]
      [Webster 1913 Suppl.]

   4. Someone who is not very intelligent or not interested in
      culture.

   Syn: yokel, rube, hick, hayseed, bumpkin, chawbacon.
        [WordNet 1.5] Yahweh
        Jahve
        Jahveh

WordNet (r) 3.0 (2006):

yahoo
    n 1: a person who is not very intelligent or interested in
         culture [syn: yokel, rube, hick, yahoo, hayseed,
         bumpkin, chawbacon]
    2: one of a race of brutes resembling men but subject to the
       Houyhnhnms in a novel by Jonathan Swift
    3: a widely used search engine for the web that finds
       information, news, images, products, finance

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

YAHOO
       Yet Another Hierarchically Officious Oracle (WWW)


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

Yahoo

    Yet Another Hierarchical
   Officious/Obstreperous/Odiferous/Organized Oracle.

   (Or a member of a race of brutes in Swift's Gulliver's Travels
   who have the form and all the vices of man, or an uncouth or
   rowdy person).

   Probably the biggest hierarchical index of the World-Wide
   Web.  Originally at Stanford University, Yahoo moved to its
   own site in April 1995.  It allows you to move up and down the
   heirarchy, to search it and to suggest additions.  It also
   features "What's New", "What's Popular", "What's Cool" and a
   random link.

   (http://yahoo.com/).

   (1995-04-05)