From plenty, taking one instance (7)
I believe the answer is:
example
'one instance' is the definition.
('example' can be a synonym of 'instance')
'from plenty' is the wordplay.
'from' becomes 'ex'.
'plenty' becomes 'ample' (I've seen this before).
'ex'+'ample'='EXAMPLE'
'taking' acts as a link.
(Other definitions for example that I've seen before include "Illustration or model" , "Punishment" , "Case in point" , "Fact that illustrates a general rule" , "Instance or illustration" .)