c.1380, from O.Fr. plungier
(c.1140), from V.L. *plumbicare
"to heave the lead," from L. plumbum
"lead" (see plumb
). Original notion perhaps is of a sounding lead or a fishing net weighted with lead. Fig. use in take the plunge
"commit oneself" is from 1845. Plunger
as a mechanism is from 1777. Plunging neckline
attested from 1949.