Crossword Genius

Expletive called for when a hole appears (4)

Ross

I believe the answer is:

darn

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'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" .)

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