Lovely day with eastern radiance briefly complete (10)
I believe the answer is:
delightful
'lovely' is the definition.
(thesaurus)
'day with eastern radiance briefly complete' is the wordplay.
'day' becomes 'd'.
'with eastern' becomes 'e' (I am not sure about the 'with' bit.).
'radiance' becomes 'light' (I've seen this before).
'briefly' means to remove the last letter.
'complete' becomes 'full' ('full' is associated in meaning with 'complete').
'full' with its final letter taken away is 'ful'.
'd'+'e'+'light'+'ful'='DELIGHTFUL'
(Other definitions for delightful that I've seen before include "Greatly pleasing" , "Pretty" , "Charming" .)