A divinely expressed wish (8)
I believe the answer is:
godspeed
'a divinely expressed wish' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
This is the entire clue.
Can you help me to learn more?
(Other definitions for godspeed that I've seen before include "Blessing or good wishes to traveller" , "parting statement" , "Word on parting" , "Farewell wish" , "Expression of good wishes to one starting a journey" .)