Purposeful muse (10)
I believe the answer is:
deliberate
This clue is a double definition.
'purposeful' is the first definition.
(thesaurus)
'muse' is the second definition.
(deliberating is a kind of musing)
(Other definitions for deliberate that I've seen before include "Done intentionally" , "Purposeful" , "Taking careful thought" , "Carefully thought out" , "Consider - intentional" .)