There are a number of ways to show the prompt of widen.  A child's grin widens as he sees his mother.  A person's eyes widen when they are surprised.  The city is widening the road to help the flow of traffic.  I captured this sailboat as it was leaving the harbor.  The river widened before him as he moved further from the harbor.  

What comes to your mind when you think of the word widen?