The gallery to close with some luck (7)
I believe the answer is:
godsend
'some luck' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'the gallery to close' is the wordplay.
'the gallery' becomes 'gods' (I've seen this before).
'to close' becomes 'end' (I've seen this before).
'gods'+'end'='GODSEND'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for godsend that I've seen before include "Something unexpected but welcome" , "Stroke of good fortune" , "Stroke of luck" , "Sudden happening that brings good fortune" , "Very welcome thing" .)