Banker welcoming Harry? Don't hold your breath! (6)
I believe the answer is:
exhale
'don't hold your breath' is the definition.
(I've seen this in another clue)
'banker welcoming harry?' is the wordplay.
'banker' becomes 'exe' (I've seen this before).
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'harry?' becomes 'hal' (Hal can be a nickname for Harry or Henry).
'exe' placed around 'hal' is 'EXHALE'.
(Other definitions for exhale that I've seen before include "produce emissions" , "let breath out" , "Breathe out" , "Joint of chicken" , "Emit breath" .)