It strikes one as a mild expletive (4)

I believe the answer is:

blow

I'm a little stuck... Click here to teach me more about this clue!

'it strikes one as a mild expletive' is the definition.
The definition suggests a singular noun which matches the answer.

This is all the clue.

Can you help me to learn more?

(Other definitions for blow that I've seen before include "Powerful stroke; completely bungle (an opportunity)" , "Setback" , "haymaker, perhaps" , "Shock; sound (a horn)" , "Hit - disappointment" .)

I've seen this clue in The Globe and Mail, The Telegraph and The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.