Correct spelling for the English word "buyest" is [bˈa͡ɪəst], [bˈaɪəst], [b_ˈaɪ_ə_s_t] (IPA phonetic alphabet).
The word "buyest" is the second person singular form of the verb "buy" in the archaic language, Old English. It comes from the Old English word "bycgan" which means "to buy" or "to acquire in exchange for money". The term "buyest" was commonly used in Middle English, but later fell out of use in Modern English as the language evolved.