casket
n. countable C2 Proficiency US //ˈkæskət// UK //kˈɑːskɪt// cas·ket
n. a small, decorative box used for keeping valuable items like jewelry or letters. In American English, it is also a common word for a coffin used at a funeral.
n. a small chest or box, often of fine workmanship, for holding jewels, letters, or other valuables. In North American usage, it serves as the standard term for a coffin.
She kept her grandmother's gold ring in a small velvet casket.
The museum display featured an ornate silver casket used by the queen to store her private correspondence.
Probably from Norman cassette. Possibly reformed by analogy with cask, thus analyzable as cask + -et. Doublet of cassette.
Usage
In British English, the 'jewelry box' sense remains primary; in American English, it almost exclusively refers to a coffin.