“so-long, kid,” he called, as his head sank to the level of the sidewalk.
As we parted he amused us by saluting and saying "Well, so-long!"
Presently they mounted, and Bud, with a loud “so-long” and a wave of the hand to some of the punchers, turned south.
"so-long, Davey," the Schoolmaster called from the verandah.
"so-long, boys," was a not infrequent remark as the noose tightened.
Now I reckon I'll bid you so-long and good-luck, and be on my way.
so-long, fellows; see you first thing in the morning, Merritt.
Nor does the poetry of ancient Greece show us the so-long vaunted delicacy of the sex.
Carson climbed into the engine-cab, with a shout: “so-long bhoy!”
The next moment, with a nonchalant “so-long,” the parting of the plains, he had dug the spurs into his horse and ridden away.
parting salutation, 1860, of unknown origin, perhaps from a German idiom (cf. 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, cf. 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!Whitman's friend and fan William Sloane Kennedy, wrote in 1923:
Remember my words -- I may again return,
I love you -- I depart from materials;
I am as one disembodied, triumphant, dead.
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.
To be convinced of the value of something or someone; strongly favor or accept: It took me a half hour to get sold on the job (1928+)