Flourish with a leap (6)
I believe the answer is:
abound
'flourish' is the definition.
(I've seen this before)
'with a leap' is the wordplay.
'with' means one lot of letters go next to another.
'leap' becomes 'bound' (bounding is a kind of leaping).
'a' put next to 'bound' is 'ABOUND'.
(Other definitions for abound that I've seen before include "Be plentiful, be present on great quantities" , "Exist in large numbers" , "Be plentiful, proliferate" , "Be plentiful, say fish in river" , "Exist in large quantities" .)