The Collaborative International Dictionary of English v.0.48:

Occur \Oc*cur"\, v. i. [imp. & p. p. Occurred; p. pr. & vb. n.
   Occurring.] [L. occurrere, occursum; ob (see Ob-) +
   currere to run. See Course.]
   1. To meet; to clash. [Obs.]
      [1913 Webster]

            The resistance of the bodies they occur with.
                                                  --Bentley.
      [1913 Webster]

   2. To go in order to meet; to make reply. [Obs.]
      [1913 Webster]

            I must occur to one specious objection. --Bentley.
      [1913 Webster]

   3. To meet one's eye; to be found or met with; to present
      itself; to appear.
      [1913 Webster]

            In Scripture, though the word heir occur, yet there
            is no such thing as "heir" in our author's sense.
                                                  --Locke.
      [1913 Webster]

   4. To happen; to take place; as, I will write if opportunity
      occurs.
      [1913 Webster]

   5. To come to the mind; to arise in the mind; to suggest
      itself; to be presented to the imagination or memory; --
      of an idea or thought; as, it never occurred to me to call
      John to ask.
      [1913 Webster +PJC]

            There doth not occur to me any use of this
            experiment for profit.                --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

occur
    v 1: come to pass; "What is happening?"; "The meeting took place
         off without an incidence"; "Nothing occurred that seemed
         important" [syn: happen, hap, go on, pass off,
         occur, pass, fall out, come about, take place]
    2: come to one's mind; suggest itself; "It occurred to me that
       we should hire another secretary"; "A great idea then came to
       her" [syn: occur, come]
    3: to be found to exist; "sexism occurs in many workplaces";
       "precious stones occur in a large area in Brazil"