Break stringed instrument case in three (7)
I believe the answer is:
violate
'break' is the definition.
(synonyms)
'stringed instrument case in three' is the wordplay.
'stringed instrument' becomes 'viola' (viola is a kind of stringed instrument).
'case in' suggests removing the centre (the letters which encase the word are used).
'three' with its middle taken out is 'te'.
'viola'+'te'='VIOLATE'
(Other definitions for violate that I've seen before include "Break in on; disregard" , "Desecrate, despoil" , "Profane" , "Infringe; defile" , "Treat sacred place with disrespect, or break vow" .)