Part of record in a Latin service book (7)
I believe the answer is:
ordinal
'service book' is the definition.
(I've seen this before)
'part of record in a latin' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'ORDINAL' is hidden within 'record in a latin'.
(Other definitions for ordinal that I've seen before include "Indicating position in sequence - iron lad (anag)" , "Numeral indicating rank order" , "Relating to series order" , "Ninth, maybe" , "Maybe first" .)