Opportunus, which had the general meaning of 'favourable, timely' in Latin , originally applied to winds at sea, 'towards the port' being just what a mariner would see as 'timely and favourable' (or opportune).
Opportunity is formed from the related noun, opportunitas, meaning 'fitness, convenience (in general)' and , specifically, ' a fit, opportune or favourable time,an advantage which offers itself ' [Lewis and Short ' A Latin Dictionary' ]