Beginning to embrace left is unforeseen (9)
I believe the answer is:
startling
'unforeseen' is the definition.
(thesaurus)
'beginning to embrace left' is the wordplay.
'beginning' becomes 'starting' ('start' can be a synonym of 'begin').
'to embrace' indicates putting letters inside.
'left' becomes 'l' (common abbreviation).
'starting' placed around 'l' is 'STARTLING'.
'is' is the link.
(Other definitions for startling that I've seen before include "Causing shock" , "Producing sudden alarm" , "Astonishing or shocking" , "Remarkable" , "Very surprising, astonishing" .)