The Collaborative International Dictionary of English v.0.48:

Modifier \Mod"i*fi`er\, n.
   1. One who, or that which, modifies. --Hume.
      [1913 Webster]

   2. (Gram.) A word or phrase that modifies another word,
      phrase, or sentence, usually by limiting the scope or
      restricting the meaning of the sentence element modified.
      [PJC]

WordNet (r) 3.0 (2006):

modifier
    n 1: a content word that qualifies the meaning of a noun or verb
         [syn: modifier, qualifier]
    2: a moderator who makes less extreme or uncompromising
    3: a person who changes something; "an inveterate changer of the
       menu" [syn: changer, modifier]
    4: a gene that modifies the effect produced by another gene
       [syn: modifier, modifier gene]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "modifier":
   IC analysis, agent, alterant, alterative, alterer, appositive,
   attribute, attributive, catalyst, catalytic agent, complement,
   construction modifier, cutting, deep structure, direct object,
   ferment, filler, form-function unit, function,
   immediate constituent analysis, indirect object, innovationist,
   innovator, introducer, leaven, levels, modificator, object,
   phrase structure, precursor, predicate, qualifier, ranks,
   shallow structure, slot, slot and filler, strata, structure,
   subject, surface structure, syntactic analysis,
   syntactic structure, syntactics, syntax, tagmeme, transformer,
   transmogrifier, underlying structure, word arrangement, word order,
   yeast



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

modifier

    An operation that alters the state of an
   object.  Modifiers often have names that begin with "set"
   and corresponding selector functions whose names begin with
   "get".

   (1998-01-12)