"without speech or noise," 1560s, from silent (adj.) + -ly (2).
Entries linking to silently
silent adj.
c. 1500, "without speech, not speaking," from Latin silentem (nominative silens) "still, calm, quiet," present participle of silere "be quiet or still" (see silence (n.)). The meaning "free from noise or sound" is from 1580s.
Of letters in a word, "not sounded or pronounced," c. 1600. In the looser sense of "of few words," by 1840. In reference to films without recorded sound, 1914.
The phrase strong, silent (type) is attested from 1905. Silent majority in the political sense of "mass of people whose moderate views are not publicly expressed and thus overlooked" is first attested 1955 in a British context and was used by John F. Kennedy but is most associated in U.S. with the rhetoric of the Nixon administration (1969-74).
It is time for America's silent majority to stand up for its rights, and let us remember the American majority includes every minority. America's silent majority is bewildered by irrational protest. [Spiro T. Agnew, May 9, 1969]
In Victorian use, the phrase meant "the dead" (by 1874; compare Roman use of the noun plural of "silent" to mean "the dead"). In one 14c. text, the Latin phrase meaning "one who is silent" is translated by a beere stille.
-ly 2
common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).
Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.