The Collaborative International Dictionary of English v.0.48:

Origin \Or"i*gin\, n. [F. origine, L. origo, -iginis, fr. oriri
   to rise, become visible; akin to Gr. 'orny`nai to stir up,
   rouse, Skr. [.r], and perh. to E. run.]
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   1. The first existence or beginning of anything; the birth.
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            This mixed system of opinion and sentiment had its
            origin in the ancient chivalry.       --Burke.
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   2. That from which anything primarily proceeds; the fountain;
      the spring; the cause; the occasion.
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   3. (Anat.) The point of attachment or end of a muscle which
      is fixed during contraction; -- in contradistinction to
      insertion.
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   Origin of coordinate axes (Math.), the point where the axes
      intersect. See Note under Ordinate.
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   Syn: Commencement; rise; source; spring; fountain;
        derivation; cause; root; foundation.

   Usage: Origin, Source. Origin denotes the rise or
          commencement of a thing; source presents itself under
          the image of a fountain flowing forth in a continuous
          stream of influences. The origin of moral evil has
          been much disputed, but no one can doubt that it is
          the source of most of the calamities of our race.
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                I think he would have set out just as he did,
                with the origin of ideas -- the proper starting
                point of a grammarian, who is to treat of their
                signs.                            --Tooke.
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                Famous Greece,
                That source of art and cultivated thought
                Which they to Rome, and Romans hither, brought.
                                                  --Waller.
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WordNet (r) 3.0 (2006):

origin
    n 1: the place where something begins, where it springs into
         being; "the Italian beginning of the Renaissance"; "Jupiter
         was the origin of the radiation"; "Pittsburgh is the source
         of the Ohio River"; "communism's Russian root" [syn:
         beginning, origin, root, rootage, source]
    2: properties attributable to your ancestry; "he comes from good
       origins" [syn: origin, descent, extraction]
    3: an event that is a beginning; a first part or stage of
       subsequent events [syn: origin, origination, inception]
    4: the point of intersection of coordinate axes; where the
       values of the coordinates are all zero
    5: the source of something's existence or from which it derives
       or is derived; "the rumor had its origin in idle gossip";
       "vegetable origins"; "mineral origin"; "origin in sensation"
    6: the descendants of one individual; "his entire lineage has
       been warriors" [syn: lineage, line, line of descent,
       descent, bloodline, blood line, blood, pedigree,
       ancestry, origin, parentage, stemma, stock]

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "origin":
   A, alpha, ancestry, babyhood, base, basis, beginning, beginnings,
   birth, birthplace, blast-off, blood, childhood, commencement,
   comparative linguistics, conception, cradle, creation,
   cutting edge, dawn, dawning, derivation, descent, edge, eponymy,
   establishment, etymology, extraction, flying start, folk etymology,
   foundation, fount, fountain, fresh start, freshman year, genealogy,
   genesis, grass roots, head, heritage, historical linguistics,
   inauguration, inception, inchoation, incipience, incipiency,
   incunabula, infancy, institution, jump-off, kick-off, launch,
   launching, leading edge, lineage, maternity, nascence, nascency,
   nativity, new departure, oncoming, onset, opening, original,
   origination, origins, outbreak, outset, parentage, parturition,
   paternity, pedigree, pregnancy, provenance, provenience, radical,
   radix, rise, root, running start, semantic history, send-off,
   setting in motion, setting-up, source, square one, start,
   start-off, starting point, stem, stock, take-off, taproot, well,
   wellspring, whence, word history, youth