The Collaborative International Dictionary of English v.0.48:

Combine \Com*bine"\, v. i.
   1. To form a union; to agree; to coalesce; to confederate.
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            You with your foes combine,
            And seem your own destruction to design --Dryden.
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            So sweet did harp and voice combine.  --Sir W.
                                                  Scott.
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   2. To unite by affinity or natural attraction; as, two
      substances, which will not combine of themselves, may be
      made to combine by the intervention of a third.
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   3. (Card Playing) In the game of casino, to play a card which
      will take two or more cards whose aggregate number of pips
      equals those of the card played.
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   Combining weight (Chem.), that proportional weight, usually
      referred to hydrogen as a standard, and for each element
      fixed and exact, by which an element unites with another
      to form a distinct compound. The combining weights either
      are identical with, or are multiples or submultiples of,
      the atomic weight. See Atomic weight, under Atomic, a.
      [1913 Webster]

WordNet (r) 3.0 (2006):

combining weight
    n 1: the atomic weight of an element that has the same combining
         capacity as a given weight of another element; the standard
         is 8 for oxygen [syn: equivalent, equivalent weight,
         combining weight, eq]