Traitor, into Old English, to give speech (5)
I believe the answer is:
orate
'give speech' is the definition.
(I've seen this before)
'traitor into old english' is the wordplay.
'traitor' becomes 'rat' (I've seen this before).
'into' means one lot of letters goes inside another.
'old english' becomes 'oe'.
'rat' inserted into 'oe' is 'ORATE'.
'to' is the link.
(Other definitions for orate that I've seen before include "Make a flowery speech" , "make speeches" , "Speak publicly" , "Lecture" , "Make a formal speech" .)