Is plentiful, as about to leap (7)
I believe the answer is:
abounds
'is plentiful' is the definition.
('abound' can be a synonym of 'be plentiful')
'as about to leap' is the wordplay.
'about' is an insertion indicator.
'to leap' becomes 'bound' (bounding is a kind of leaping).
'as' enclosing 'bound' is 'ABOUNDS'.
(Other definitions for abounds that I've seen before include "Exists in large quantities" , "Flourishes" , "Exists in large numbers or amounts" , "Is all over the place" , "Is plentiful" .)