Most sacred presenter conceals fib (7)
I believe the answer is:
holiest
'most sacred' is the definition.
('holy' can be similar in meaning to 'sacred')
'presenter conceals fib' is the wordplay.
'presenter' becomes 'host' (as in the host of a TV show).
'conceals' means one lot of letters goes inside another.
'fib' becomes 'lie' (a fib is a lie).
'host' going around 'lie' is 'HOLIEST'.
(Other definitions for holiest that I've seen before include "Most pious" , "Most resembling sacred work" , "most befitting to worship" , "Most divine" , "superlatively untouchable" .)