The Collaborative International Dictionary of English v.0.48:

Relation \Re*la"tion\ (r?-l?"sh?n), n. [F. relation, L. relatio.
   See Relate.]
   1. The act of relating or telling; also, that which is
      related; recital; account; narration; narrative; as, the
      relation of historical events.
      [1913 Webster]

            ??????oet's relation doth well figure them. --Bacon.
      [1913 Webster]

   2. The state of being related or of referring; what is
      apprehended as appertaining to a being or quality, by
      considering it in its bearing upon something else;
      relative quality or condition; the being such and such
      with regard or respect to some other thing; connection;
      as, the relation of experience to knowledge; the relation
      of master to servant.
      [1913 Webster]

            Any sort of connection which is perceived or
            imagined between two or more things, or any
            comparison which is made by the mind, is a relation.
                                                  --I. Taylor.
      [1913 Webster]

   3. Reference; respect; regard.
      [1913 Webster]

            I have been importuned to make some observations on
            this art in relation to its agreement with poetry.
                                                  --Dryden.
      [1913 Webster]

   4. Connection by consanguinity or affinity; kinship;
      relationship; as, the relation of parents and children.
      [1913 Webster]

            Relations dear, and all the charities
            Of father, son, and brother, first were known.
                                                  --Milton.
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   5. A person connected by cosanguinity or affinity; a
      relative; a kinsman or kinswoman.
      [1913 Webster]

            For me . . . my relation does not care a rush. --Ld.
                                                  Lytton.
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   6. (Law)
      (a) The carrying back, and giving effect or operation to,
          an act or proceeding frrom some previous date or time,
          by a sort of fiction, as if it had happened or begun
          at that time. In such case the act is said to take
          effect by relation.
      (b) The act of a relator at whose instance a suit is
          begun. --Wharton. Burrill.
          [1913 Webster]

   Syn: Recital; rehearsal; narration; account; narrative; tale;
        detail; description; kindred; kinship; consanguinity;
        affinity; kinsman; kinswoman.
        [1913 Webster]

WordNet (r) 3.0 (2006):

relation
    n 1: an abstraction belonging to or characteristic of two
         entities or parts together
    2: the act of sexual procreation between a man and a woman; the
       man's penis is inserted into the woman's vagina and excited
       until orgasm and ejaculation occur [syn: sexual
       intercourse, intercourse, sex act, copulation,
       coitus, coition, sexual congress, congress, sexual
       relation, relation, carnal knowledge]
    3: a person related by blood or marriage; "police are searching
       for relatives of the deceased"; "he has distant relations
       back in New Jersey" [syn: relative, relation]
    4: an act of narration; "he was the hero according to his own
       relation"; "his endless recounting of the incident eventually
       became unbearable" [syn: relation, telling, recounting]
    5: (law) the principle that an act done at a later time is
       deemed by law to have occurred at an earlier time; "his
       attorney argued for the relation back of the amended
       complaint to the time the initial complaint was filed" [syn:
       relation back, relation]
    6: (usually plural) mutual dealings or connections among persons
       or groups; "international relations"

The Free On-line Dictionary of Computing (19 January 2023):

relation

   1.  A subset of the product of two sets,

    R : A x B

   If (a, b) is an element of R then we write

    a R b

   meaning a is related to b by R.

   A relation may be: reflexive (a R a), symmetric (a R b =>
   b R a), transitive (a R b & b R c => a R c), antisymmetric
   (a R b & b R a => a = b) or total (a R b or b R a).

   Relations are most commonly between two sets (binary
   relations) but could be between more than two.

   See equivalence relation, partial ordering, pre-order,
   total ordering.

   2.  A table in a relational database.

   (1995-02-28)