What is the etymology of bouillon cubes? What other word can I use?
The Wiktionary page for bouillon describes the etymology well. The immediate origin of the word is quite clearly French, and is cognate with boil in English.
First attested 1656, from French bouillir (“to boil”), from Old French boillir, from Latin bullīre, present active infinitive of bulliō (“I bubble, boil”), from bulla (“bubble”).
A bouillon cube is simply a bit of dehydrated bullion (broth) shaped into a cube, so it can be easily added to a liquid to quickly season a broth.
(Why do I feel I'm on the Food and Cooking StackExchange site..?)