Necessitate a note before Latin revision (6)
I believe the answer is:
entail
'necessitate' is the definition.
(I know that entail is a type of necessitate)
'a note before latin revision' is the wordplay.
'a note' becomes 'e' (musical note).
'before' means one lot of letters go next to another.
'revision' indicates anagramming the letters.
'latin' anagrammed gives 'ntail'.
'e'+'ntail'='ENTAIL'
(Other definitions for entail that I've seen before include "Restriction on inheritance" , "Cut" , "Cause" , "Involve (something) as an inevitable consequence" , "Late in (anag.)" .)