faith

1. (archaic) Alternative form of in faith (“really, truly”).Examples: "“How wonderfully,” said Vincent, “your city dignities unloose the tongue: directly a man has been a mayor, he thinks himself qualified for a Tully at least. Faith, Venables asked me one day, what was the Latin for spouting? and I told him, ‘hippomanes, or a raging humour in mayors.’”"; "'Faith, friend,' he says, 'that was a nasty fall for a fellow that has supped weel. Where might your road be gaun to?'"

1. (obsolete) Ellipsis of by my faith.