He's crotchety and has a bad cold in the head (5)
I believe the answer is:
crank
'he's crotchety and has a bad' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'cold in the head' is the wordplay.
'cold' becomes 'C' (eg on taps).
'in the head' becomes 'rank' (I can't justify this - if you can you should believe this answer much more).
'c'+'rank'='CRANK'
Can you help me to learn more?
(Other definitions for crank that I've seen before include "Turn (engine handle); eccentric" , "Person of eccentric habits" , "Turn a handle - weirdo" , "Person with strange ideas, or machine part" , "Wind (up) - oddball" .)