Relieve complete dunderhead straying in wander (9)
I believe the answer is:
alleviate
'relieve' is the definition.
(synonyms)
'complete dunderhead straying in wander' is the wordplay.
I cannot quite see how this works, but
'complete' could be 'all' (similar in meaning) and 'all' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for alleviate that I've seen before include "Lighten" , "moderate" , "Lessen severity" , "To mollify" , "Make (pain) less intense" .)