Opportunity for luck (6)
I believe the answer is:
chance
I believe this clue is a double definition.
'opportunity' is the first definition.
(I know that opportunity can be written as chance)
'for luck' is the second definition.
(synonyms)
(Other definitions for chance that I've seen before include "The unpredictable element of existence" , "Probability" , "he unpredictable element of life" , "Serendipity" , "Risk the fortune" .)