A cold leads to horrible ear pain (4)
I believe the answer is:
ache
'pain' is the definition.
(ache is a kind of pain)
'a cold leads to horrible ear' is the wordplay.
'a cold' becomes 'ac' (I've seen this in other clues**).
'leads to' suggests taking the first letters.
The first letters of 'horrible ear' is 'he'.
'ac'+'he'='ACHE'
(Other definitions for ache that I've seen before include "Similar" , "agony" , "Dull prolonged pain" , "Persistent dull pain" , "Each (anag.)" .)