I had to return Spider? Most awful! (6)
I believe the answer is:
direst
'most awful' is the definition.
('dire' can be a synonym of 'awful')
'i had to return spider?' is the wordplay.
'i had' becomes 'i'd' (contraction).
'to return' is a reversal indicator.
'spider?' becomes 'rest' (I can't explain this - if you can you should give a lot more credence to this answer).
'id' back-to-front is 'di'.
'di'+'rest'='DIREST'
Can you help me to learn more?
(Other definitions for direst that I've seen before include "Most horrific" , "far from ideal" .)