Roman emperor giving a month to us (8)
I believe the answer is:
augustus
'roman emperor' is the definition.
(I know that Augustus is a roman emperor)
'giving a month to us' is the wordplay.
'giving' means one lot of letters go next to another.
'a month' becomes 'August' (August is an example).
'august'+'us' is 'AUGUSTUS'.
(Other definitions for augustus that I've seen before include "old ruler" , "The first Roman emperor - month named after him" , "head for Rome" , "one whose name was John?" , "Successor to Julius Caesar" .)