[1] : The Collaborative International Dictionary of English v.0.48

ultimatum \ul`tima"tum\ u^l`ti^m=a"tu^m, n.; pl. e.
   ultimatums u^l`ti^m=a"tu^mz, l. ultimata. nl.
   see ultimate.
   1. a final proposition, concession, or condition; especially,
      the final propositions, conditions, or terms, offered by
      either of the parties in a diplomatic negotiation; the
      most favorable terms that a negotiator can offer, the
      rejection of which usually puts an end to the hesitation.
      1913 webster

   2. a final demand, the rejection of which may lead to a
      resort to force or other compelling action by the party
      presenting the ultimatum. in international diplomacy, an
      ultimatum may be used as by the demanding country as a
      signal to other countries that it gave the other country a
      seemingly reasonable opportunity to avoid a war; in this
      way, the demanding country may seek to avoid
      responsibility for starting a war.
      pjc
      1913 webster
see also:
ultimatums ultimata ultimate 

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Ultimatums, definition of term: Ultimatums
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