The Collaborative International Dictionary of English v.0.48:

Widen \Wid"en\, v. t. [imp. & p. p. Widened; p. pr. & vb. n.
   Widening.]
   To make wide or wider; to extend in breadth; to increase the
   width of; as, to widen a field; to widen a breach; to widen a
   stocking.
   [1913 Webster]