Anu's word today is forsooth. Interesting that sooth part. Basically from the PIE root *es- 'to be', sooth is related to Skt satya 'truth' and German Sünde (English sin) 'sin', literally 'is is (true)'. (Also, Skt swastika < su- 'good' + esti 'it is + -ka nominalizing suffix.) In the same semantic ballpark (field), there's very and verily from Latin verus 'truth' and truth < true + -th; true is related to tree (and Gk drous 'oak' and Celtic druid) and originally meant straight. (Carpenters still talk about a board being true.)

[And a tip of the hat to Dr Bill for nudging me.]