Expletive called for when a hole appears (4)
I believe the answer is:
darn
'expletive' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for darn that I've seen before include "Mend with 17s - mild expletive" , "Mend by stitching - damn!" , "Repair (sock)" , "Mend a hole in a sock" , "Sew" .)