From Longman Dictionary of Contemporary Englishseeing as (how)seeing as (how)informal (also seeing that)ALTHOUGH used before giving a reason for what you are saying ‘I might as well do something useful, seeing as I’m back, ’ she said. → see
Examples from the Corpus
seeing as (how)• That seems believable, too, seeing as how he no longer can take out his frustrations on Sundays.• This struck them as strange, seeing as how it was only just after four in the morning.• I just slipped that in seeing as how you congratulated me on my history.• Well, seeing as how you just lost one of your men, you might think about hiring some one to replace him.• And seeing as it was my brainchild, would you not say it was possibly the best commercial of all time?• The D-32 is very Martin D-28 in character - not surprising, seeing as that's what it basically is.• I thought you might like that, seeing as you're so keen on birds and that.• But, seeing as you won't tell me anything, I have to use other sources. 