The origins of the word Dream are somewhat obscure:
dream \Dream\ (dr[=e]m), n. [Akin to OS. dr[=o]m, D. droom, G. traum, Icel. draumr, Dan. & Sw. dr["o]m; cf. G. tr["u]gen to deceive, Skr. druh to harm, hurt, try to hurt. AS. dre['a]m joy, gladness, and OS. dr[=o]m joy are, perh., different words; cf. Gr. qry^los noise.] 1. The thoughts, or series of thoughts, or imaginary transactions, which occupy the mind during sleep; a sleeping vision.