Over a kiss (6)
'over' is the definition.
'a kiss' is the wordplay.
I cannot really understand how this works, but
'a' is within the answer.
The remaining letters 'cross' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for across that I've seen before include "14 of these clues are", "sort of clue?", "Horizontally", "Transversely", "Towards the other side of".)