Las conjunciones as, though, even if, even though, however, though, although expresan una concesión.

21.3.7.1 as / though = a pesar de que, con lo ...
He didn't eat the cake though he was hungry.
No comió la tarta a pesar de tener mucha hambre.
Busy as they were they didn't notice the thunderstorm outside.
Con lo ocupado que estuvieron no notaron la tormenta fuera.
Sunny though it was, we stayed inside.
A pesar de que hacía sol, se quedaron dentro.