Spike's cat outside looking miserable (6)
I believe the answer is:
moping
'looking miserable' is the definition.
I can't tell whether this defines the answer.
'spike's cat outside' is the wordplay.
'spike' becomes 'pin' (pinning is a kind of spiking).
'cat' becomes 'mog' (informal British term).
'outside' indicates putting letters inside (some letters go outside others).
'pin' inserted within 'mog' is 'MOPING'.
Can you help me to learn more?
(Other definitions for moping that I've seen before include "Sulking or mooning about" , "Wandering about in low spirits" , "brooding" , "Being dejected and apathetic" , "Moving about listlessly" .)