Meditate on (4)
I believe the answer is:
muse
'meditate on' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for muse that I've seen before include "Contemplation" , "Ponder on one of nine" , "Ponder or meditate" , "Source of artistic inspiration" , "Contemplate -- a goddess of the liberal arts" .)