coast (n.)youdaoicibaDictYouDict[coast 词源字典]
"margin of the land," early 14c.; earlier "rib as a part of the body" (early 12c.), from Old French coste "rib, side, flank; slope, incline;" later "coast, shore" (12c., Modern French côte), from Latin costa "a rib," perhaps related to a root word for "bone" (compare Old Church Slavonic kosti "bone," also see osseous).

Latin costa developed a secondary sense in Medieval Latin of "the shore," via notion of the "side" of the land, as well as "side of a hill," and this passed into Romanic (Italian costa "coast, side," Spanish cuesta "slope," costa "coast"), but only in the Germanic languages that borrowed it is it fully specialized in this sense (Dutch kust, Swedish kust, German Küste, Danish kyst). French also used this word for "hillside, slope," which led to verb meaning "sled downhill," first attested 1775 in American English. Expression the coast is clear (16c.) is an image of landing on a shore unguarded by enemies.[coast etymology, coast origin, 英语词源]
knight (n.)youdaoicibaDictYouDict
Old English cniht "boy, youth; servant, attendant," common West Germanic (cognates: Old Frisian kniucht, Dutch knecht, Middle High German kneht "boy, youth, lad," German Knecht "servant, bondman, vassal"), of unknown origin. The plural in Middle English sometimes was knighten. Meaning "military follower of a king or other superior" is from c. 1100. Began to be used in a specific military sense in Hundred Years War, and gradually rose in importance until it became a rank in the nobility 16c. The chess piece so called from mid-15c. Knight in shining armor in figurative sense is from 1917, from the man who rescues the damsel in distress in romantic dramas (perhaps especially "Lohengrin"). Knights of Columbus, society of Catholic men, founded 1882 in New Haven, Connecticut, U.S.; Knights of Labor, trade union association, founded in Philadelphia, 1869; Knights of Pythias, secret order, founded in Washington, 1864.
savior (n.)youdaoicibaDictYouDict
c. 1300, "one who delivers or rescues from peril," also a title of Jesus Christ, from Old French sauveour, from Late Latin salvatorem (nominative salvator) "a saver, preserver" (source also of Spanish salvador, Italian salvatore), from salvatus, past participle of salvare "to save" (see save (v.)). In Christian sense, a translation of Greek soter "savior." Replaced Old English hælend, literally "healing," noun use of present participle of hælan (see heal).