Boss taking call with top-notch listening device (7,3)
I believe the answer is:
hearing aid
'listening device' is the definition.
'boss taking call with top-notch' is the wordplay.
'boss' becomes 'head' (synonyms).
'taking' is an insertion indicator.
'call with' becomes 'ring' (telephone call. I am not sure about the 'with' bit.).
'top notch' becomes 'ai' (resembles 'Ar', old-fashioned term for excellent).
'ring'+'ai'='ringai'
'head' placed around 'ringai' is 'HEARING-AID'.
Can you help me to learn more?
(Other definitions for hearing aid that I've seen before include "Earpiece" , "asset in court?" , "Ear trumpet" , "Amplifier for ear" , "Help for the partially deaf" .)