Return record featuring small exercise book (6)
I believe the answer is:
gospel
'book' is the definition.
(I've seen this before)
'return record featuring small exercise' is the wordplay.
'return' shows that the letters should be reversed in order.
'record' becomes 'log' (logging is a kind of recording).
'featuring' indicates putting letters inside.
'small' becomes 's' (abbreviation - e.g. clothes size).
'exercise' becomes 'pe' (Physical Education).
'log' backwards is 'gol'.
's'+'pe'='spe'
'gol' placed around 'spe' is 'GOSPEL'.
(Other definitions for gospel that I've seen before include "One in quartet" , "Christian doctrine" , "God's honest truth" , "Unquestionable truth - church doctrine" , "Type of music" .)