Considered problem raised by editor (5)
I believe the answer is:
mused
'considered' is the definition.
The definition and answer can be both related to thinking as well as being past participle verbs.
Perhaps there's an association between them I don't understand?
'problem raised by editor' is the wordplay.
'problem' becomes 'sum' (as in a mathematical problem).
'raised by' shows that the letters should be reversed in order.
'editor' becomes 'ed' (abbreviation).
'sum' back-to-front is 'mus'.
'mus'+'ed'='MUSED'
Can you help me to learn more?
(Other definitions for mused that I've seen before include "Fuddled" , "Closer" , "Reflected or pondered" , "'Meditated, mulled (5)'" , "Contemplated" .)