Elastic band held by agent (7)
I believe the answer is:
springy
'elastic' is the definition.
(similar in meaning)
'band held by agent' is the wordplay.
'band' becomes 'ring' (a ring is a band of metal).
'held by' indicates putting letters inside.
'agent' becomes 'spy' (spy is a kind of agent).
'ring' placed into 'spy' is 'SPRINGY'.
(Other definitions for springy that I've seen before include "Elastic, resilient" , "jumpy" , "With bounce" .)