Yours, Etc.: Origins and Uses of 8 Sign-Offs
"as, in the capacity of," from Latin qua "where? on which side? at which place? which way? in what direction?" figuratively "how? in what manner? by what method?; to what extent? in what degree?" correlative pronomial adverb of place, from PIE *kwo-, stem of relative and interrogative pronouns (cf. Old English hwa "who;" see who).