Back up religious type suppressing a Gaelic language (7)
I believe the answer is:
reverse
'back up' is the definition.
(I've seen this before)
'religious type suppressing a gaelic language' is the wordplay.
'religious type' becomes 'rev' (short for reverend).
'suppressing' is a charade indicator (letters next to each other) (in a down clue, some letters go on top of others).
'a gaelic language' becomes 'erse' (term for the Scottish or Irish language).
'rev'+'erse'='REVERSE'
(Other definitions for reverse that I've seen before include "Turn back to front" , "Do u-turn to reserve" , "Countermand" , "Travel backwards" , "Britannia's place" .)