Elastic band stuck in clock (7)
I believe the answer is:
springy
'elastic' is the definition.
('springy' can be similar in meaning to 'elastic')
'band stuck in clock' is the wordplay.
'band' becomes 'ring' ('ring' can be a synonym of 'band').
'stuck in' indicates putting letters inside.
'clock' becomes 'spy' (both can mean to notice or spot something).
'ring' placed within 'spy' is 'SPRINGY'.
(Other definitions for springy that I've seen before include "jumpy" , "With bounce" , "Elastic, resilient" .)