Evidence of cold inert gas introduced to drink (5)
I believe the answer is:
rheum
'evidence of cold' is the definition.
'rheum' can be an answer for 'cold' (I've seen this before). I am unsure of the 'evidence of' bit.
'inert gas introduced to drink' is the wordplay.
'inert gas' becomes 'He' (chemical symbol for helium, an inert gas).
'introduced to' is an insertion indicator.
'drink' becomes 'rum' (rum is a kind of drink).
'he' placed within 'rum' is 'RHEUM'.
Can you help me to learn more?
(Other definitions for rheum that I've seen before include "Watery stuff" , "Tears of a cold" , "sign of illness" , "nasal drops" , "Watery discharge; sounds like space" .)