1. [n]  a member of the Religious Society of Friends founded by George Fox (the Friends have never called themselves Quakers)
2. [n]  a person with whom you are acquainted; "I have trouble remembering the names of all my acquaintances"; "we are friends of the family"
3. [n]  an associate who provides assistance; "he's a good ally in fight"; "they were friends of the workers"
4. [n]  a person you know well and regard with affection and trust; "he was my best friend at the university"
5. [n]  a person who backs a politician or a team etc.; "all their supporters came out for the game"; "they are friends of the library"

Friend
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1. \Friend\ (fr[e^]nd), n. [OR. frend, freond, AS.
   fre['o]nd, prop. p. pr. of fre['o]n, fre['o]gan, to love;
   akin to D. vriend friend, OS. friund friend, friohan to love,
   OHG. friunt friend, G. freund, Icel. fr[ae]ndi kinsman, Sw.
   fr["a]nde. Goth. frij[=o]nds friend, frij[=o]n to love.
   [root]83. See {Free}, and cf. {Fiend}.]
   1. One who entertains for another such sentiments of esteem,
      respect, and affection that he seeks his society aud
      welfare; a wellwisher; an intimate associate; sometimes,
      an attendant.
            Want gives to know the flatterer from the friend.
                                                  --Dryden.
            A friend that sticketh closer than a brother.
                                                  --Prov. xviii.
                                                  24.
   2. One not inimical or hostile; one not a foe or enemy; also,
      one of the same nation, party, kin, etc., whose friendly
      feelings may be assumed. The word is some times used as a
      term of friendly address.
            Friend, how camest thou in hither?    --Matt. xxii.
                                                  12.
   3. One who looks propitiously on a cause, an institution, a
      project, and the like; a favorer; a promoter; as, a friend
      to commerce, to poetry, to an institution.
   4. One of a religious sect characterized by disuse of outward
      rites and an ordained ministry, by simplicity of dress and
      speech, and esp. by opposition to war and a desire to live
      at peace with all men. They are popularly called Quakers.
            America was first visited by Friends in 1656. --T.
                                                  Chase.
   5. A paramour of either sex. [Obs.] --Shak.
   {A friend} {at court or in court}, one disposed to act as a
      friend in a place of special opportunity or influence.
   {To be friends with}, to have friendly relations with. ``He's
      . . . friends with C[ae]sar.'' --Shak.
   {To make friends with}, to become reconciled to or on
      friendly terms with. ``Having now made friends with the
      Athenians.'' --Jowett (Thucyd.).
   

2. \Friend\, v. t. [imp. & p. p. {Friended}; p. pr. & vb. n.
   {Friending}.]
   To act as the friend of; to favor; to countenance; to
   befriend. [Obs.]
         Fortune friends the bold.                --Spenser.
   

Relationship between classes in the language C++.