tomorrow (adv.) Look up tomorrow at Dictionary.com
mid-13c., to morewe, from Old English to morgenne "on (the) morrow," from to "at, on" (see to) + morgenne, dative of morgen "morning" (see morn, also morrow). As a noun from late 14c. Written as two words until 16c., then as to-morrow until early 20c.