The Collaborative International Dictionary of English v.0.48:

Relevance \Rel"e*vance\ (r?l"?*vans), Relevancy \Rel"e*van*cy\
   (-van*s?), n.
   1. The quality or state of being relevant; pertinency;
      applicability.
      [1913 Webster]

            Its answer little meaning, little relevancy bore.
                                                  --Poe.
      [1913 Webster]

   2. (Scots Law) Sufficiency to infer the conclusion.
      [1913 Webster]

WordNet (r) 3.0 (2006):

relevance
    n 1: the relation of something to the matter at hand [syn:
         relevance, relevancy] [ant: irrelevance,
         irrelevancy]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "relevance":
   account, admissibility, advantage, affective meaning, affinity,
   applicability, application, appositeness, appropriateness,
   aptitude, aptness, bearing, coloring, concern, concernment,
   connection, connotation, consequence, denotation, drift, effect,
   essence, extension, felicity, fitness, fittedness, force,
   germaneness, gist, grammatical meaning, idea, impact, implication,
   import, intension, interest, lexical meaning, literal meaning,
   materiality, meaning, overtone, pertinence, pith, point,
   practical consequence, propriety, purport, qualification,
   range of meaning, real meaning, reference, referent, regard,
   relatedness, relation, respect, scope, semantic cluster,
   semantic field, sense, service, serviceability, significance,
   signification, significatum, signifie, span of meaning, spirit,
   structural meaning, substance, suitability, suitableness, sum,
   sum and substance, symbolic meaning, tenor, tie-in,
   totality of associations, transferred meaning, unadorned meaning,
   undertone, use, usefulness, utility, value



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

relevance

    A measure of how closely a given object
   (file, web page, database record, etc.) matches a user's
   search for information.

   The relevance algorithms used in most large web search
   engines today are based on fairly simple word-occurence
   measurement: if the word "daffodil" occurs on a given page,
   then that page is considered relevant to a query on the word
   "daffodil"; and its relevance is quantised as a factor of the
   number of times the word occurs in the page, on whether
   "daffodil" occurs in title of the page or in its META
   keywords, in the first N words of the page, in a heading,
   and so on; and similarly for words that a stemmer says are
   based on "daffodil".

   More elaborate (and resource-expensive) relevance algorithms
   may involve thesaurus (or synonym ring) lookup; e.g. it
   might rank a document about narcissuses (but which may not
   mention the word "daffodil" anywhere) as relevant to a query
   on "daffodil", since narcissuses and daffodils are basically
   the same thing.  Ditto for queries on "jail" and "gaol", etc.

   More elaborate forms of thesaurus lookup may involve
   multilingual thesauri (e.g. knowing that documents in Japanese
   which mention the Japanese word for "narcissus" are relevant
   to your search on "narcissus"), or may involve thesauri (often
   auto-generated) based not on equivalence of meaning, but on
   word-proximity, such that "bulb" or "bloom" may be in the
   thesaurus entry for "daffodil".

   Word spamming essentially attempts to falsely increase a web
   page's relevance to certain common searches.

   See also subject index.

   (1997-04-09)