Widen, as pupils (6)
I believe the answer is:
dilate
'widen as pupils' 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 "Tailed (anag)" , "Widen in detail as pupils may" , "Enlarge or widen, like pupils perhaps" , "Expand in detail" , "Widen as eyes may" .)