Inaugurate by oath (5,2)
I believe the answer is:
swear in
'inaugurate by oath' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for swear in that I've seen before include "Administer official oath" , "Admit to office" , "Get into office" , "Inaugurate by oath" , "bring candidate to office" .)