morrow n.

"the first part of the day, the morning," late 14c., contracted from Middle English morwen, morghen, from Old English (Mercian) margen (dative marne), earlier morgen (dative morgne) "morning, forenoon, sunrise," from Proto-Germanic *murgana- "morning" (source also of Old Saxon morgan, Old Frisian morgen, Middle Dutch morghen, Dutch morgen, Old High German morgan, German Morgen, Gothic maurgins), from PIE *merk-, perhaps from root *mer- "to blink, twinkle" (source of Lithuanian mirgėti "to blink"). By late 19c. relegated to poetry.

greeting salutation, c. 1400, from good (adj.) + morning. Earlier good morwe (late 14c.), from morrow.

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.