Q: How did the phrase “so long” get to mean goodbye?
A: The colloquial expression “so long” (meaning goodbye) has been around since the mid-19th century, according to the Oxford English Dictionary.
Many etymologists have tried to pin down the origin of the expression, but it’s still in doubt. The phrase apparently first appeared in print in the mid-19th century in a poem by Walt Whitman, aptly titled “So Long!”
The poem is about death and leave-taking, and was first published as the final poem in an 1860 edition of Leaves of Grass. The expression “so long” appears several times, as in these examples:
“While my pleasure is yet at the full, I whisper, So long! / And take the young woman’s hand, and the young man’s hand, for the last time.” And later: “So long! / Remember my words.” (The italics are the poet’s.)
Where did Whitman get the phrase? A friend of his, William Sloane Kennedy, has written that Whitman said he’d heard it “greatly used among sailors, sports, & prostitutes.” (The source of this is an article on a linguistic website, Onomasiology Online.)
Interestingly, there are similar-sounding salutations in other languages, including German (so lange), Hebrew (shalom), Norwegian (så lenge), Swedish (så länge), Arabic (salaam), and Irish Gaelic (slan), and even Malay (selang).
To make a long story short, we don’t know where the phrase originally came from, but my money is on the German or Scandinavian connections.
It seems likely that German or Scandinavian immigrants brought the expression with them and that it became working-class vernacular before spreading.