古英語のscitan, shit, faecesから、原語ゲルマン語*のskitana, defecationから、skei, to cut, to separateから、語源はshed, sheath, scienceと同じ。語源比較 turd.
Alle te filt of his magh ['maw'] salle breste out atte his fondament for drede. ["Cursor Mundi," early 14c.]
The expression [the shit hits the fan] is related to, and may well derive from, an old joke. A man in a crowded bar needed to defecate but couldn't find a bathroom, so he went upstairs and used a hole in the floor. Returning, he found everyone had gone except the bartender, who was cowering behind the bar. When the man asked what had happened, the bartender replied, 'Where were you when the shit hit the fan?' [Hugh Rawson, "Wicked Words," 1989]