The French embracing one in unalloyed delight (8)
I believe the answer is:
pleasure
'delight' is the definition.
('pleasure' can be a synonym of 'delight')
'the french embracing one in unalloyed' is the wordplay.
'the french' becomes 'les' (les is the in french**).
'embracing' means one lot of letters goes inside another.
'one' becomes 'a'.
'in' indicates putting letters inside.
'unalloyed' becomes 'pure' ('pure' can be similar in meaning to 'unalloyed').
'les' placed around 'a' is 'leas'.
'leas' placed inside 'pure' is 'PLEASURE'.
(Other definitions for pleasure that I've seen before include "A desirable emotion" , "Delight, happiness" , "amusement" , "Delectation, delight" , "A very desirable feeling" .)