Breathy line in chat, possibly (5)
I believe the answer is:
aitch
'breathy line in chat possibly' is the definition.
I can't judge whether this defines the answer.
'line in chat possibly' is the wordplay.
'line' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'possibly' indicates anagramming the letters.
'chat' is an anagram of 'atch'.
'i' placed within 'atch' is 'AITCH'.
Can you help me to learn more?
(Other definitions for aitch that I've seen before include "The letter h in full" , "that I will immediately succeed" , "that may be dropped" , "8th letter of the alphabet" , "the start of hives?" .)