A dash just before take-off (5,4)

I believe the answer is:

minus sign

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

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

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for minus sign that I've seen before include "indication of negativity?" , "indicating deduction!" , "Subtraction indicator" , "Symbol indicating subtraction" , "Maths operator" .)

I've seen this clue in the Evening Standard.

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.