Gas put a tiny bit of taste into negroni cocktail (8)
I believe the answer is:
nitrogen
'gas' is the definition.
(I know that nitrogen is a type of gas)
'a tiny bit of taste into negroni cocktail' is the wordplay.
'a tiny bit of' suggests taking the first letters.
'into' is an insertion indicator.
'cocktail' indicates an anagram.
The first letter of 'taste' is 't'.
'negroni' is an anagram of 'nirogen'.
't' inserted into 'nirogen' is 'NITROGEN'.
'put' acts as a link.
(Other definitions for nitrogen that I've seen before include "creates much atmosphere" , "Much of what we take in" , "Inert nog is an inert gas" , "Gaseous element" , "Commonest atmospheric gas" .)