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, tomorwe, from Old English to morgenne "on (the) morrow, on the day following the present one;" from to "at, on" (see to) + morgenne, dative of morgen "morning" (see morn, also morrow). The form tomorn also survived in Middle English and is said in OED (1989) to be vernacular in the North of England.

Written as two words until 16c., then as to-morrow until early 20c. As a noun from late 14c., "the day after the present day;" hence "the (near) future," a sense attested by 1898.

After a piano selection by Miss Smythe, C.H. Fraser delivered his address on "The World's Tomorrow." The speaker declared that the world's tomorrow will be a better day materially, intellectually, morally and spiritually than today. ... Not organic unity, but great harmony among great diversities will be the religion of the world's tomorrow. The morning of that sweeter, brighter, better day is already dawning. [report on the Twin City Chautauqua in the Champaign (Illinois) Daily News, Aug. 26, 1898]

To do something as if there were no tomorrow "recklessly" is by 1839.