First opportunity (7)
I believe the answer is:
opening
This clue is a double definition.
'first' is the first definition.
(similar in meaning)
'opportunity' is the second definition.
(I know that opening is a type of opportunity)
(Other definitions for opening that I've seen before include "First -- beginning" , "Aperture or opportunity" , "Yawning" , "Aperture or first night" , "Space, gap; beginning" .)