Tennis for the unattached? (7)

I believe the answer is:

singles

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

'tennis' is the definition.
(I know that singles is a type of tennis)

I cannot understand how the rest of the clue works.

(Other definitions for singles that I've seen before include "Form of tennis" , "Ones" , "Type of tennis match" , "Non-return tickets" .)

I've seen this clue in The Mirror.

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.