The Collaborative International Dictionary of English v.0.48:

Usage \Us"age\, n. [F. usage, LL. usaticum. See Use.]
   [1913 Webster]
   1. The act of using; mode of using or treating; treatment;
      conduct with respect to a person or a thing; as, good
      usage; ill usage; hard usage.
      [1913 Webster]

            My brother
            Is prisoner to the bishop here, at whose hands
            He hath good usage and great liberty. --Shak.
      [1913 Webster]

   2. Manners; conduct; behavior. [Obs.]
      [1913 Webster]

            A gentle nymph was found,
            Hight Astery, excelling all the crew
            In courteous usage.                   --Spenser.
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   3. Long-continued practice; customary mode of procedure;
      custom; habitual use; method. --Chaucer.
      [1913 Webster]

            It has now been, during many years, the grave and
            decorous
            usage of Parliaments to hear, in respectful silence,
            all expressions, acceptable or unacceptable, which
            are uttered from the throne.          --Macaulay.
      [1913 Webster]

   4. Customary use or employment, as of a word or phrase in a
      particular sense or signification.
      [1913 Webster]

   5. Experience. [Obs.]
      [1913 Webster]

            In eld [old age] is both wisdom and usage.
                                                  --Chaucer.
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   Syn: Custom; use; habit.

   Usage: Usage, Custom. These words, as here compared,
          agree in expressing the idea of habitual practice; but
          a custom is not necessarily a usage. A custom may
          belong to many, or to a single individual. A usage
          properly belongs to the great body of a people. Hence,
          we speak of usage, not of custom, as the law of
          language. Again, a custom is merely that which has
          been often repeated, so as to have become, in a good
          degree, established. A usage must be both often
          repeated and of long standing. Hence, we speak of a
          "hew custom," but not of a "new usage." Thus, also,
          the "customs of society" is not so strong an
          expression as the "usages of society." "Custom, a
          greater power than nature, seldom fails to make them
          worship." --Locke. "Of things once received and
          confirmed by use, long usage is a law sufficient."
          --Hooker. In law, the words usage and custom are often
          used interchangeably, but the word custom also has a
          technical and restricted sense. See Custom, n., 3.
          [1913 Webster]
          [1913 Webster]

WordNet (r) 3.0 (2006):

usage
    n 1: the act of using; "he warned against the use of narcotic
         drugs"; "skilled in the utilization of computers" [syn:
         use, usage, utilization, utilisation, employment,
         exercise]
    2: accepted or habitual practice [syn: custom, usage,
       usance]
    3: the customary manner in which a language (or a form of a
       language) is spoken or written; "English usage"; "a usage
       borrowed from French"

Moby Thesaurus II by Grady Ward, 1.0:

155 Moby Thesaurus words for "usage":
   acceptance, acceptation, acception, active use, adjectival phrase,
   antonym, appliance, application, articulation, automatism,
   bad habit, bon ton, care, ceremony, characteristic, choice,
   choice of words, clause, composition, conformity, construction,
   consuetude, consumption, convenance, convention, creature of habit,
   custodianship, custom, dialect, diction, employ, employment,
   established way, etiquette, exercise, exertion, expression,
   fashion, folkway, force of habit, form, formality, formulation,
   free form, good use, grammar, guidance, guiding, habit,
   habit pattern, habitude, handling, hard usage, hard use,
   headed group, homograph, homonym, homophone, idiom, idiotism,
   ill use, language, langue, lead, lexeme, lingo, lingua,
   linguistic form, locution, logos, management, manipulation, manner,
   manner of speaking, manners, means of dealing, metonym,
   minimum free form, misuse, monosyllable, mores, noun phrase,
   observance, operation, paragraph, parlance, parole, pattern,
   peculiar expression, peculiarity, period, personal usage,
   phrasal idiom, phrase, phraseology, phrasing, polysyllable,
   practice, praxis, preference, prescription, procedure, proceeding,
   process, proper thing, received meaning, rhetoric, ritual,
   rough usage, routine, second nature, sentence, set phrase,
   social convention, speech, standard behavior, standard phrase,
   standard usage, standing custom, stereotype, stereotyped behavior,
   stewardship, syllable, synonym, syntactic structure, talk, term,
   time-honored practice, tongue, tradition, treatment, trick,
   turn of expression, turn of phrase, use, use of words, using up,
   usus loquendi, utterance, verb complex, verb phrase, verbalism,
   verbiage, verbum, vocable, way, way of speaking, what is done,
   wont, wonting, word, word-group, wordage, wording, wrong use



Bouvier's Law Dictionary, Revised 6th Ed (1856):

USAGE. Long and uniform practice. In its most extensive meaning this term
includes custom and prescription, though it differs from them in a narrower
sense, it is applied to the habits, modes, and course of dealing which are
observed in trade generally, as to all mercantile transactions, or to some
particular branches of trade.
     2. Usage of trade does not require to be immemorial to establish it; if
it be known, certain, uniform, reasonable, and not contrary to law, it is
sufficient. But evidence of a few instances that such a thing has been done
does not establish a usage. 3 Watts, 178; 3 Wash. C. C. R. 150; 1 Gallis.
443; 5 Binn. 287; 9 Pick. 426; 4 B. & Ald. 210; 7 Pet. 1; 2 Wash. C. C. R.
7.
     3. The usages of trade afford ground upon which a proper construction
may be given to contracts. By their aid the indeterminate intention of
parties and the nature and extent of their contracts arising from mere
implications or presumptions, and act of an equivocal character may be
ascertained; and the meaning of words and doubtful expressions may become
known. 2 Mete. 65; 2 Sumn. 569; 2 G. & J. 136; 13 Pick. 182; Story on Ag.
Sec. 77; 2 Kent, Com. 662, 3d ed.; 5 Wheat. 326; 2 Car. & P. 525; 3 B. &
Ald. 728; Park. on Ins. 30; 1 Marsh. Ins. 186, n. 20; 1 Caines, 45 Gilp.
356, 486; 1 Edw. Ch. R. 146; 1 N. & M. 519; 15 Mass. 433; 1 Rill, R. 270;
Wright, R. 573; Pet. C. C. R. 230; 5 Hamm. 436 6 Pet. 715; 2 Pet. 148; 6
Porter, 123 1 Hall, 612; 9 Mass. 155; 9 Wheat. 582 11 Wheat. 430; 1 Pet. 25,
89.
     4. Courts will not readily adopt these usages, because they are not
unfrequently founded in mistake. 2 Sumn. 377. See 3 Chitt. Pr. 55; Story,
Confl. of Laws, Sec. 270; 1 Dall. 178; Vaugh. 169, 383; Bouv. Inst. Index,
h.t.



The Devil's Dictionary (1881-1906):

USAGE, n.  The First Person of the literary Trinity, the Second and
Third being Custom and Conventionality.  Imbued with a decent
reverence for this Holy Triad an industrious writer may hope to
produce books that will live as long as the fashion.