From Latin "sicut" which means something like "it was this way", "like that", "exactly this way".
It's usually used in the bracket in the text besides the word which could be recognized as written in the wrong way;
Mostly used to a quoted spelling mistake, implying for the reader that it isn't our mistake, but it was this way in the original.
The air ticket form Chicago to Shanghai costs about $1500 (sic!);
As he wrote in his message "tihs will be a looong juorney" (sic!);