(that) [conjunction], [informal] seeing as, not standard seeing as how conjunction, [conjunction] - considering or accepting the fact that; asSeeing that we need to arrive by twelve o'clock, we'd better leave at nine.We may as well go to the concert, seeing as (how) we've already paid for the tickets.
SEEING
Meaning of SEEING in English
Cambridge English vocab. Кембриджский английский словарь. 2012