Cough or breathe on them! (3)
I believe the answer is:
hem
'cough' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'breathe on them' is the wordplay.
'HEM' is hidden in amongst the letters.
However, I am uncertain 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 "It draws attention to" , "Stitched edge of garment" , "Double-backed border of a garment" , "may attract attention" , "Finished edge of a piece of cloth" .)