Privately, assistant receives the final sacraments (5)
I believe the answer is:
aside
'privately' is the definition.
(thesaurus)
'assistant receives the final sacraments' is the wordplay.
'assistant' becomes 'aide' (aide is a kind of assistant).
'receives' means one lot of letters goes inside another.
'the final' indicates one should take the final letters.
The final letter of 'sacraments' is 's'.
'aide' placed around 's' is 'ASIDE'.
(Other definitions for aside that I've seen before include "I.e. sad (anag.)" , "Privately, apart" , "Remark not for hearing" , "Digression" , "Words spoken apart in an undertone" .)