Mike's small ring? (10)
I believe the answer is:
microphone
'mike's' is the definition.
(synonyms)
'small ring?' is the wordplay.
'small' becomes 'micro' (similar in meaning).
'ring?' becomes 'phone' ('phone' can be a synonym of 'ring').
'micro'+'phone'='MICROPHONE'
(Other definitions for microphone that I've seen before include "Device to pick up and transmit sounds" , "Sound receiver" .)