Give priestly approval to the grade below A minus (5)
I believe the answer is:
bless
'give' is the definition.
(thesaurus)
'below a minus' is the wordplay.
'below' becomes 'b' (this could be a standard abbreviation which I don't know about).
'a minus' becomes 'less' (I've seen this in another clue).
'b'+'less'='BLESS'
'priestly approval to the grade' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for bless that I've seen before include "set aside for holy purpose?" , "Make holy" , "Approve of" , "Consecrate; be thankful for" , "perform consecration" .)