Cause to expand (6)
I believe the answer is:
dilate
'cause to expand' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dilate that I've seen before include "Enlarge - detail (anag)" , "Widen, spread out" , "Widen as eyes may" , "Become wider, pupil of the eye perhaps" , "explain more fully" .)