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, 1884 (n.); hence, the verb meaning "shower (someone) with boos" (1885).
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 before 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," in Notes and Queries, 4th series, vi, Sept. 10, 1870]
Old English felan "to touch or have a sensory experience of; perceive, sense (something)," in late Old English "have a mental perception," from Proto-Germanic *foljanan (source also of Old Saxon gifolian, Old Frisian fela, Dutch voelen, Old High German vuolen, German fühlen "to feel," Old Norse falma "to grope"), which is of uncertain origin, possibly from a PIE *pal- "to touch, feel, shake, strike softly" (source also of Greek psallein "to pluck" the harp), or from PIE root *pel- (5) "to thrust, strike, drive."
In Germanic languages, the specific word for "perceive by sense of touch" has tended to evolve to apply to the emotions. The connecting notion might be "perceive through senses which are not referred to any special organ." Sense of "be conscious of a tactile sensation, sense pain, pleasure, illness, etc.; have an emotional experience or reaction," developed by c. 1200, also "have an opinion or conviction;" that of "to react with sympathy or compassion" is from mid-14c. Meaning "to try by touch" is from early 14c. From late 14c. as "know (something) beforehand, to have foreknowledge of." To feel like "want to" attested from 1829.
Proto-Indo-European root meaning "to collect, gather," with derivatives meaning "to speak" on the notion of "to gather words, to pick out words."
It forms all or part of: alexia; analects; analogous; analogue; analogy; anthology; apologetic; apologue; apology; catalogue; coil; colleague; collect; college; collegial; Decalogue; delegate; dialect; dialogue; diligence; doxology; dyslexia; eclectic; eclogue; elect; election; epilogue; hapax legomenon; homologous; horology; ideologue; idiolect; intelligence; lectern; lectio difficilior; lection; lector; lecture; leech (n.2) "physician;" legacy; legal; legate; legend; legible; legion; legislator; legitimate; lesson; lexicon; ligneous; ligni-; logarithm; logic; logistic; logo-; logogriph; logopoeia; Logos; -logue; -logy; loyal; monologue; neglect; neologism; philology; privilege; prolegomenon; prologue; relegate; sacrilege; select; syllogism; tautology; trilogy.
It is the hypothetical source of/evidence for its existence is provided by: Greek legein "to say, tell, speak, declare; to count," originally, in Homer, "to pick out, select, collect, enumerate;" lexis "speech, diction;" logos "word, speech, thought, account;" Latin legere "to gather, choose, pluck; read," lignum "wood, firewood," literally "that which is gathered," legare "to depute, commission, charge," lex "law" (perhaps "collection of rules"); Albanian mb-ledh "to collect, harvest;" Gothic lisan "to collect, harvest," Lithuanian lesti "to pick, eat picking;" Hittite less-zi "to pick, gather."