Principal boy embraces dame at last (4)
I believe the answer is:
lead
'principal' is the definition.
('lead' can be a synonym of 'principal')
'boy embraces dame at last' is the wordplay.
'boy' becomes 'lad' (lad is a kind of boy**).
'embraces' is an insertion indicator.
'at last' suggests the final letters.
The final letter of 'dame' is 'e'.
'lad' going around 'e' is 'LEAD'.
(Other definitions for lead that I've seen before include "Travel in front of" , "First news item" , "Primary" , "1 down, symbol Pb" , "Heavy metal; star" .)