Leave nothing to be desired (7)
I believe the answer is:
satisfy
'leave' is the definition.
The answer and definition can be both to do with fundamental existence as well as being verbs in their base form.
Maybe you can see a link between them that I don't see?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for satisfy that I've seen before include "Meet the needs of (someone)" , "Satiate" , "Be good enough for" , "Meet, comply with" , "Meet the desires of" .)