A singular shoe (of _grass"?) (7)

I believe the answer is:

sneaker

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

'a singular shoe' is the definition.
'sneaker' can be an answer for 'shoe' (sneaker is a kind of shoe). I am not sure about the 'a singular' bit.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for sneaker that I've seen before include "Casual shoe" , "Trainer (shoe)" , "Soft shoe" , "Canvas shoe" , "one tending to go unnoticed?" .)

I've seen this clue in the Evening Standard.

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