1461, "small box for jewels, etc.," possibly formed as a dim. of Eng. cask,
or from Norm.-Fr. cassette,
from M.Fr. casset
). Meaning of "coffin" is Amer.Eng., probably euphemistic, first attested 1849.
"Caskets! a vile modern phrase, which compels a person ... to shrink ... from the idea of being buried at all." [Hawthorne, 1863]