A pointed reminder that you’re late? (4)

I believe the answer is:

spur

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'a pointed reminder' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I can't see?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for spur that I've seen before include "footballer?" , "slip road" , "Goad as for a horse" , "This provokes sudden movement!" , "Sharp pointed projection" .)

I've seen this clue in the Evening Standard.

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