Form a mental image of (8)
I believe the answer is:
envisage
'form a mental image of' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for envisage that I've seen before include "Visualise - vine's age (anag)" , "Conceive of, imagine" , "Contemplate, imagine" , "See" , "Mentally picture" .)