Random opportunity (6)
I believe the answer is:
chance
This clue is a double definition.
'random' is the first definition.
(similar in meaning)
'opportunity' is the second definition.
(I know that opportunity can be written as chance)
(Other definitions for chance that I've seen before include "'Fate, luck, fortune (6)'" , "part of Monopoly" , "Possibility - opportunity" , "Luck or accident" , "Risk doing (something)" .)