Cough a little or breathe on them! (3)
I believe the answer is:
hem
'cough a little' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'breathe on them' is the wordplay.
'HEM' is hidden in amongst the letters.
But, I am uncertain how the hidden word is indicated.
'or' is the link.
Can you help me to learn more?
(Other definitions for hem that I've seen before include "Sewn edge to fabric" , "Double-backed cloth border" , "Finished edge of a piece of cloth" , "Border; fringe" , "try to attract attention" .)