It's tasteful, but may suggest an unhealthy atmosphere (3,4)
I believe the answer is:
pea soup
'unhealthy atmosphere' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'it's tasteful but may suggest an' is the wordplay.
I cannot really see how this works, but
'an' could be 'a' and 'a' is present in the answer.
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' is found in the remaining letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for pea soup that I've seen before include "very hazy situation" , "Liquid vegetable-based dish (like thick fog)" , "Food - thick yellow fog" , "Green-coloured starter" , "Green broth" .)