The Collaborative International Dictionary of English v.0.48:

Derivation \Der`i*va"tion\, n. [L. derivatio: cf. F.
   d['e]rivation. See Derive.]
   1. A leading or drawing off of water from a stream or source.
      [Obs.] --T. Burnet.
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   2. The act of receiving anything from a source; the act of
      procuring an effect from a cause, means, or condition, as
      profits from capital, conclusions or opinions from
      evidence.
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            As touching traditional communication, . . . I do
            not doubt but many of those truths have had the help
            of that derivation.                   --Sir M. Hale.
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   3. The act of tracing origin or descent, as in grammar or
      genealogy; as, the derivation of a word from an Aryan
      root.
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   4. The state or method of being derived; the relation of
      origin when established or asserted.
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   5. That from which a thing is derived.
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   6. That which is derived; a derivative; a deduction.
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            From the Euphrates into an artificial derivation of
            that river.                           --Gibbon.
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   7. (Math.) The operation of deducing one function from
      another according to some fixed law, called the law of
      derivation, as the operation of differentiation or of
      integration.
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   8. (Med.) A drawing of humors or fluids from one part of the
      body to another, to relieve or lessen a morbid process.
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   9. The formation of a word from its more original or radical
      elements; also, a statement of the origin and history of a
      word.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

derivation
    n 1: the source or origin from which something derives (i.e.
         comes or issues); "he prefers shoes of Italian derivation";
         "music of Turkish derivation"
    2: (historical linguistics) an explanation of the historical
       origins of a word or phrase [syn: deriving, derivation,
       etymologizing]
    3: a line of reasoning that shows how a conclusion follows
       logically from accepted propositions
    4: (descriptive linguistics) the process whereby new words are
       formed from existing words or bases by affixation; "`singer'
       from `sing' or `undo' from `do' are examples of derivations"
    5: inherited properties shared with others of your bloodline
       [syn: ancestry, lineage, derivation, filiation]
    6: drawing of fluid or inflammation away from a diseased part of
       the body
    7: drawing off water from its main channel as for irrigation
    8: the act of deriving something or obtaining something from a
       source or origin