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.
However, I'm unsure how this is indicated.
'or' acts as a 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" .)