Old school operator terminated return segment (5)
I believe the answer is:
'old school' is the definition.
(I've seen this in another clue)
'operator terminated return segment' is the wordplay.
'RETRO' is hidden back-to-front in amongst the letters.
However, I'm uncertain how this is indicated.
Can you help me to learn more?
(Other definitions for retro that I've seen before include "reminding us of the past" , "recapturing the past" , "Prefix for old-style" , "Reliving the past" , "Backward looking" .)