The Collaborative International Dictionary of English v.0.48:

Overween \O`ver*ween"\, v. t. [AS. oferw[=e]nian. See Over,
   and Ween.]
   To think too highly or arrogantly; to regard one's own
   thinking or conclusions too highly; hence, to be egotistic,
   arrogant, or rash, in opinion; to think conceitedly; to
   presume.
   [1913 Webster]

         They that overween,
         And at thy growing virtues fret their spleen. --Milton.
   [1913 Webster]