The Antique Dictionary

a small, glass-paneled, locking cabinet for the securing and display of fine liquors

 

The name comes from Greek mythology where Tantalus was punished by being forced see food and drink and not be able to access either.  He stood in a pool of water beneath the low branches of a fruit tree which he could see but not reach, and the water of the pool would recede if he tried to take a drink.  This myth is the basis of the word tantalizing.

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Some confuse a tantalus with a “cave a liqueur” which was also a locked box for liqueur, but a cave a liqueur will have solid-paneled rather than glass-paneled sides.  This makes their contents both out of reach and unseen, thereby not reflecting the character myth of Tantalus who could see but not reach what he desired.