Unsure how to combat the shivers (5)
I believe the answer is:
vague
'unsure' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I don't see?
'to combat the shivers' is the wordplay.
'to combat' becomes 'v' (I can't explain this - if you can you should believe this answer much more).
'the shivers' becomes 'ague' (I've seen this before).
'v'+'ague'='VAGUE'
'how' is the link.
Can you help me to learn more?
(Other definitions for vague that I've seen before include "Amorphous" , "Indistinct or not clearly expressed" , "Imprecise (in thought)" , "not focused" , "Indefinite" .)