initialism (acronym) from shit out of luck (though sometimes euphemised), 1917, World War I military slang. "Applicable to everything from death to being late for mess" [R. Lord, "Captain Boyd's Battery A.E.F."]
Rwanda
-ry
rye
-s
s'mores
S.O.L.
S.P.Q.R.
S.T.D.
S.W.A.T.
s/he
*sa-
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