grandyoudaoicibaDictYouDict[grand 词源字典]
grand: [16] The original Latin word for ‘big’ was magnus (as in magnify, magnitude, etc). However, it also had grandis. This not only denoted great physical size; it also had connotations of moral greatness or sublimity, and in addition often carried the specialized meaning ‘full-grown’. This last, together with a possibly etymologically connected Greek brénthos ‘pride’ and Old Church Slavonic gradi ‘breast’ suggest that its underlying meaning may be ‘swelling’.

French (grand) and Italian and Spanish (grande) have taken it over as their main adjective for ‘big’, but in English it remains a more specialized word, for things or people that are ‘great’ or ‘imposing’. Its use for denoting family relationships separated by two generations, as in grandmother, was adopted from Old French, and goes back, in the case of grandame and grandsire, to the 13th century, well before the independent adjective grand itself was borrowed.

But the underlying notion is as old as the Greeks and Romans, who used mégas and magnus in the same way.
[grand etymology, grand origin, 英语词源]
grand (adj.)youdaoicibaDictYouDict
late 14c., grant "large, big" (early 12c. in surnames), from Anglo-French graunt and directly from Old French grant, grand (10c., Modern French grand) "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," of unknown origin. In Vulgar Latin it supplanted magnus and continued in the Romanic languages. The connotations of "noble, sublime, lofty, dignified," etc., were in Latin. In English it developed a special sense of "imposing." Meaning "principal, chief, most important" (especially in titles) is from 1560s; that of "of very high or noble quality" is from 1712. As a general term of admiration, "magnificent, splendid," from 1816. Related: Grander; grandest.

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 of the Colorado River in western U.S. was so called by 1869, popularized by Maj. John Wesley Powell, scientific adventurer, who explored it; earlier it had been known as Big Canyon. For grand slam see slam (n.2).
grand (n.)youdaoicibaDictYouDict
"thousand dollars," 1915, American English underworld slang, from grand (adj.).