Horrified losing order with sound system
I believe the answer is:
hi-fi
'sound system' is the definition.
(hi-fi is a kind of sound system)
'horrified losing order' is the wordplay.
'losing' indicates named letters should be taken away.
'horrified' with 'order' removed is 'HI-FI'.
'with' acts as a link.
(Other definitions for hi-fi that I've seen before include "Sound reproduction unit" , "Good quality sound system, in short" , "Good-quality sound equipment" , "Stereo" , "High-quality sound equipment" .)