Blessing given by one disciple beneath mountain (7)
I believe the answer is:
benison
'blessing' is the definition.
(benison is a kind of blessing)
'by one disciple beneath mountain' is the wordplay.
'by' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'disciple' becomes 'son' (I've seen this in other clues).
'beneath' means one lot of letters go next to another (in a down clue).
'mountain' becomes 'ben' (ben is a kind of mountain**).
'i'+'son' is 'ison'.
'ison' after 'ben' is 'BENISON'.
'given' is the link.
(Other definitions for benison that I've seen before include "Sob, nine turn into a blessing" , "Thanksgiving" , "Benediction" .)