I leave oil on her car (5)
I believe the answer is:
carol
'i leave oil' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'on her car' is the wordplay.
'on' says to put letters next to each other.
'her' becomes 'ol' (I am not sure about this - if you are sure you should believe this answer much more).
'ol' put after 'car' is 'CAROL'.
Can you help me to learn more?
(Other definitions for carol that I've seen before include "A traditional Christmas song or hymn" , "Joyful song - girl's name" , "See 1" , "Song celebrating the birth of Jesus" , "Joyful religious song" .)