widen

To widen is to make something wider, or to become wider. A road, a river mouth, a crack in a wall.

It works both ways round without changing form, since you widen the path and the path widens. The figurative use is very common in reporting: a widening gap between rich and poor, widening the search, a widening investigation. Eyes widen in surprise, which is one of the standard gestures of English fiction. It belongs to the -en family of verbs alongside deepen, sharpen and strengthen.