Best man's embraced by old friend (7)
I believe the answer is:
optimal
'best' is the definition.
(similar in meaning)
'man's embraced by old friend' is the wordplay.
'man' becomes 'tim' (short for Timothy).
'embraced by' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'friend' becomes 'pal' (pal is a kind of friend).
'o'+'pal'='opal'
'tim' placed within 'opal' is 'OPTIMAL'.
(Other definitions for optimal that I've seen before include "couldn't be better" , "Am pilot being at best" , "top, surprisingly" , "Ideal" , "as good as can be" .)