1671, the first element perhaps an alteration of cistern (q.v.); or the whole may be an alteration of suspiral (c.1400), "drainpipe," from O.Fr. souspirail "a vent, air hole," from souspirer "breathe," from L. suspirare "breathe deep." Meaning extended to "tank at the end of the pipe," which led to folk etymology change in final syllable. Other possible etymologies: It. cesso "privy," from L. secessus "place of retirement" (in L.L. "privy, drain"); dial. suspool, from suss, soss "puddle;" or cess "a bog on the banks of a tidal river."