An indication of cold perhaps (6)
I believe the answer is:
sneeze
'an indication' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for sneeze that I've seen before include "Act of sternutation" , "Symptom of cold" , "Nasal eruption from common cold" , "React to irritation" , "Precursor to "bless you"" .)