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 really see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
The remaining letters 'lte' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'who's' acts as a 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" .)