Opus (5)
(Other definitions for dei that I've seen before include "Of God, in Latin" , "Agnus . . . - Lamb of God" .)
'opus' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for piece that I've seen before include "constituent" , "Single article" , "wedge a > bit" , "rook, perhaps" , "Castle, perhaps" .)