The Collaborative International Dictionary of English v.0.48:

Endeavor \En*deav"or\, v. t. [imp. & p. p. Endeavored; p. pr.
   & vb. n. Endeavoring.] [OE. endevor; pref. en- + dever,
   devoir, duty, F. devoir: cf. F. se mettre en devoir de faire
   quelque chose to try to do a thing, to go about it. See
   Devoir, Debt.] [Written also endeavour.]
   To exert physical or intellectual strength for the attainment
   of; to use efforts to effect; to strive to achieve or reach;
   to try; to attempt.
   [1913 Webster]

         It is our duty to endeavor the recovery of these
         beneficial subjects.                     --Ld. Chatham.
   [1913 Webster]

   To endeavor one's self, to exert one's self strenuously to
      the fulfillment of a duty. [Obs.] "A just man that
      endeavoreth himself to leave all wickedness." --Latimer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

endeavour
    n 1: a purposeful or industrious undertaking (especially one
         that requires effort or boldness); "he had doubts about the
         whole enterprise" [syn: enterprise, endeavor,
         endeavour]
    2: earnest and conscientious activity intended to do or
       accomplish something; "made an effort to cover all the
       reading material"; "wished him luck in his endeavor"; "she
       gave it a good try" [syn: attempt, effort, endeavor,
       endeavour, try]
    v 1: attempt by employing effort; "we endeavor to make our
         customers happy" [syn: endeavor, endeavour, strive]