英语词源字典 - 在线词源网站

apparition (n.)[apparition 词源字典]: c. 1500, "unclosing" (of Heaven), from Anglo-French aparicion, Old French apparition, aparoison (15c.), used in reference to the Epiphany (revealing of Christ child to the Wise Men), from Late Latin apparitionem (nominative apparitio) "an appearance," also "attendants," in classical Latin "service, servants," noun of action from past participle stem of apparere "appear" (see appear). Meaning "ghost" first recorded c. 1600; the shade of sense differentiation between appearance and apparition is that the latter tends to be unexpected or startling.[apparition etymology, apparition origin, 英语词源]
boo: expression meant to startle, early 15c., boh, "A combination of consonant and vowel especially fitted to produce a loud and startling sound" [OED, which compares Latin boare, Greek boaein "to cry aloud, roar, shout."]; as an expression of disapproval, 1801 (n.), 1816 (v.); hence, the verb meaning "shower someone with boos" (1893).

Booing was common late 19c. among London theater audiences and at British political events; In Italy, Parma opera-goers were notorious boo-birds, but the custom seems to have been little-known in America till c. 1910.

To say boo "open one's mouth, speak," originally was to say boo to a goose.
To be able to say Bo! to a goose is to be not quite destitute of courage, to have an inkling of spirit, and was probably in the first instance used of children. A little boy who comes across some geese suddenly will find himself hissed at immediately, and a great demonstration of defiance made by them, but if he can pluck up heart to cry 'bo!' loudly and advance upon them, they will retire defeated. The word 'bo' is clearly selected for the sake of the explosiveness of its first letter and the openness and loudness of its vowel. [Walter W. Skeat, "Cry Bo to a Goose, "Notes and Queries," 4th series vi Sept. 10, 1870]
conscientious objector (n.): 1896, in reference to those with religious scruples about mandatory vaccination. Military sense predominated from World War I.
After a chequered career full of startling episodes and reversals, the Vaccination Bill becomes virtually the Vaccination Act. In Parliament the hottest of the contest centred round the conscientious objector. [The Lancet, Aug. 13, 1898]
startle (v.): c. 1300, "run to and fro" (intransitive), frequentative of sterten (see start (v.)). Sense of "move suddenly in surprise or fear" first recorded 1520s. Transitive meaning "frighten suddenly" is from 1590s. The word retains more of the original meaning of start (v.). Related: Startled; startling; startlingly. As a noun from 1714.