A lot vs. Alot: 9 Grammatical Pitfalls
late 14c., grant "large, big" (early 12c. in surnames), from Anglo-French graunt and directly from Old French grant, grand (10c.) "large, tall; grown-up; great, powerful, important; strict, severe; extensive; numerous," from Latin grandis "big, great; full, abundant," also "full-grown;" figuratively "strong, powerful, weighty, severe" (perhaps cognate with Greek brenthyomai "to swagger, be haughty"). It supplanted magnus in Romanic languages; in English with a special sense of "imposing." The connotations of "noble, sublime, lofty, dignified," etc., were in Latin. As a general term of admiration, "magnificent, splendid," from 1816. Related: Grander; grandest.
The use of grand- in compounds, with the sense of "a generation older than, or younger than," is first attested c.1200, in Anglo-French graund dame "grandmother." Latin and Greek had similar usages.
Grand jury is late 15c. Grand piano from 1797. The grand tour of the principal sites of continental Europe, as part of a gentleman's education, is attested by that name from 1660s. The Grand Canyon was so called 1871 by Maj. John Wesley Powell, scientific adventurer, who explored it; earlier it had been known as Big Canyon.
"thousand dollars," 1915, American English underworld slang, from grand (adj.).
A thousand dollars; gee: A banker would scarcely call one thousand dollars ''one grand''
[1920+ Underworld & sports; said to have originated with Peaches Van Camp, a criminal who flashed such grand notes for ostentation]