grandson (n.)

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).

"male child in relation to either or both parents," Old English sunu "son, male child," also broadly "male descendant;" also "second person of the Trinity," from Proto-Germanic *sunus (source also of Old Saxon and Old Frisian sunu, Old Norse sonr, Danish søn, Swedish son, Middle Dutch sone, Dutch zoon, Old High German sunu, German Sohn, Gothic sunus "son").

The Germanic words are from PIE *su(H)nus "son" (source also of Sanskrit sunus, Greek huios, Avestan hunush, Armenian ustr, Lithuanian sūnus, Old Church Slavonic synu, Russian and Polish syn "son"), a derived noun from root *su(H)- "to give birth" (source also of Sanskrit sauti "gives birth," Old Irish suth "birth, offspring").

The sense of "person whose character partakes so much of some quality as to suggest the relation of a son to a parent" was in Old English. As "person regarded as the product of some place," 1590s.

Son of _____ as the title of a sequel to a book or movie is recorded from 1917 ("Son of Tarzan"). Most explanations for son of a gun (1708) are more than a century after its appearance. Henley (1903) describes it as meaning originally "a soldier's bastard;" Smyth's "Sailor's Word-Book" (1867) describes it as "An epithet conveying contempt in a slight degree, and originally applied to boys born afloat, when women were permitted to accompany their husbands to sea ...."