The ex who's keeping one waiting (4)
I believe the answer is:
late
'the ex' is the definition.
(I've seen this in other clues)
'keeping one waiting' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found within the answer.
The remaining letters 'lte' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'who's' is the link.
Can you help me to learn more?
(Other definitions for late that I've seen before include "Far into the night" , "Having bought it" , "No longer alive; tardy" , "Previous" , "In arrears" .)