pupilyoudaoicibaDictYouDict[pupil 词源字典]
pupil: [14] Latin pūpus and pūpa meant respectively ‘boy’ and ‘girl’ (pūpa was applied by the Swedish naturalist Linnaeus to ‘chrysalises’, the underlying link being ‘undeveloped creature’, and English adopted it as pupa [19]). The diminutive derivatives pūpillus and pūpilla denoted ‘orphan’, a sense which remained with pūpill- as it passed via Old French pupille into English as pupil. ‘Person being taught’ did not emerge until the 16th century.

The application of the word to the ‘black aperture in the eye’, which reached English in the mid-16th century, goes back to Latin pūpilla, which was also used for ‘doll’ – the notion being that if you stand close to someone and look into their eyes, you can see yourself reflected in the pupils like a little ‘doll’.

=> pupa, puppet, puppy[pupil etymology, pupil origin, 英语词源]
alligator (n.)youdaoicibaDictYouDict
1560s, lagarto (modern form attested from 1620s, with excrescent -r as in tater, feller, etc.), a corruption of Spanish el lagarto (de Indias) "the lizard (of the Indies)," from Latin lacertus (see lizard). Alligarter was an early variant. The slang meaning "non-playing devotee of swing music" is attested from 1936; the phrase see you later, alligator is from a 1956 song title.
hid (v.)youdaoicibaDictYouDict
past tense and alternative past participle of hide (v.1).
How to entangle, trammel up and snare
Your soul in mine, and labyrinth you there
Like the hid scent in an unbudded rose?
Aye, a sweet kiss -- you see your mighty woes.

[Keats, "Lamia"]
lateryoudaoicibaDictYouDict
comparative of late. Meaning "farewell" is from 1954, U.S. slang, short for see you later.
see (v.)youdaoicibaDictYouDict
Old English seon "to see, look, behold; observe, perceive, understand; experience, visit, inspect" (contracted class V strong verb; past tense seah, past participle sewen), from Proto-Germanic *sekhwan (cognates: Old Saxon, Old High German sehan, Middle High German, German sehen, Old Frisian sia, Middle Dutch sien, Old Norse sja, Gothic saihwan), from PIE root *sekw- (2) "to see," which is probably identical with *sekw- (1) "to follow" (see sequel), a root which produced words for "say" in Greek and Latin, and also words for "follow" (such as Latin sequor), but "opinions differ in regard to the semantic starting-point and sequences" [Buck]. Thus see might originally mean "follow with the eyes."

Used in Middle English to mean "behold in the imagination or in a dream" (c. 1200), "to recognize the force of (a demonstration)," also c. 1200. Sense of "escort" (as in to see (someone) home) first recorded 1607 in Shakespeare. Meaning "to receive as a visitor" is attested from c. 1500. Gambling sense of "equal a bet" is from 1590s. See you as a casual farewell first attested 1891. Let me see as a pausing statement is recorded from 1510s. To have seen everything as a hyperbolic expression of astonishment is from 1957.
When you have seen one of their Pictures, you have seen all. [Blake, c. 1811]
so long (interj.)youdaoicibaDictYouDict
parting salutation, 1860, of unknown origin, perhaps from a German idiom (compare German parting salutation adieu so lange, the full sense of which probably is something like "farewell, whilst (we're apart)"); or perhaps from Hebrew shalom (via Yiddish sholom). Some have noted a similarity to Scandinavian leave-taking phrases, such as Norwegian Adjø så lenge, Farvel så lenge, Mor'n så lenge, literally "bye so long, farewell so long, morning so long;" and Swedish Hej så länge "good-bye for now," with så länge "for now" attested since 1850 according to Swedish sources. Most etymology sources seem to lean toward the German origin.

Earlier guesses that it was a sailors' corruption of a South Pacific form of Arabic salaam are not now regarded as convincing. "Dictionary of American Slang" also adds to the list of candidates Irish slán "safe," said to be used as a salutation in parting. The phrase seems to have turned up simultaneously in America, Britain, and perhaps Canada, originally among lower classes. First attested use is in title and text of the last poem in Whitman's "Leaves of Grass" in the 1860 edition.
An unknown sphere, more real than I dream'd, more direct, darts awakening rays about me -- So long!
Remember my words -- I may again return,
I love you -- I depart from materials;
I am as one disembodied, triumphant, dead.
Whitman's friend and fan William Sloane Kennedy wrote in 1923:
The salutation of parting -- 'So long!' -- was, I believe, until recent years, unintelligible to the majority of persons in America, especially in the interior, and to members of the middle and professional classes. I had never heard of it until I read it in Leaves of Grass, but since then have quite often heard it used by the laboring class and other classes in New England cities. Walt wrote to me, defining 'so long' thus: "A salutation of departure, greatly used among sailors, sports, & prostitutes -- the sense of it is 'Till we meet again,' -- conveying an inference that somehow they will doubtless so meet, sooner or later." ... It is evidently about equivalent to our 'See you later.' The phrase is reported as used by farm laborers near Banff, Scotland. In Canada it is frequently heard; 'and its use is not entirely confined to the vulgar.' It is in common use among the working classes of Liverpool and among sailors at Newcastle-upon-Tyne, and in Dorsetshire. ... The London Globe suggests that the expression is derived from the Norwegian 'Saa laenge,' a common form of 'farewell,' au revoir. If so, the phrase was picked up from the Norwegians in America, where 'So long' first was heard. The expression is now (1923) often used by the literary and artistic classes.
SWAKyoudaoicibaDictYouDict
acronym for sealed with a kiss, attested from 1911, in a legal publication quoting a letter from 1909:
"... Well Kid I don't know nothing else to say only that I hope to see your sweet face Sat. Good by from your Dear Husban to his sweet little wife. P. S. excuse bad writing and mispelled words take all mistakes as kisses. S.W.A.K. * * *" This letter was postmarked at Des Moines October 20, 1909, addressed to Carrie Sprague at Jefferson, Iowa, and reached the latter place October 21, 1909. [State v. Manning (a conspiracy-to-lure-women-to-prostitution case), Supreme Court of Iowa, Nov. 16, 1910, reported in "Northwestern Reporter," Volume 128, 1911]
Popularized in soldiers' letters home in World War I. It probably is meant also to echo the sound of a kiss. Compare Middle English swack "a hard blow" (late 14c.).