fridujo

A container word, and a useful reminder that -uj- has three jobs rather than one. It makes containers (monujo a purse, salujo a salt cellar, cindrujo an ashtray), it makes fruit trees (pomujo an apple tree), and in the older orthography it made countries (Francujo). The country sense is the one that lost the argument, for reasons set out at length in Landoj kaj Popoloj; the container sense is alive and doing the work here. The full affix table is in word building.

The interesting part is which word won. Esperanto had frida sitting there, a Latinate root for cold that almost nobody uses in conversation, because everyday cold is malvarma. A refrigerator could perfectly well have been a malvarmujo, a cold-container, and it is not: malvarmujo never took, and the obscure root beat the transparent compound. That happens when a machine needs a name that sounds like a machine rather than a description, and frida earns its keep almost entirely inside this one word and its relatives, fridigi to refrigerate and fridigilo the cooling unit.

The freezer beside it is a frostujo, from frosto, frost. Same suffix, one root over, and a nicely literal pair: cold goes in the fridujo, frozen goes in the frostujo.