Merriam-Webster defines banquet as an elaborate, sumptuous feast held for ceremonial purposes, in honor of a person, or in recognition of some occasion or achievement. We most often hear the word in regards to a state banquet or an awards banquet. Probably the biggest reason the word is used is it sounds better than big feast for rich people.
Of course, you do not have to be rich and powerful to have a banquet, some regular folks have been known to have wedding banquets, for instance. The word has an unlikely origin, though, being that it signifies huge feasts.
Etymology of Banquet
Although some sources trace the word from the Italian word banco, the most likely source of our word banquet comes from the French word banquet which means a little bench. This word originally comes from the Germanic word bangk, which meant bench.
It is from the word bangk that we get our English word bench. But it also took a different path, becoming banc in Old French, from which the diminutive form banquet was derived.
The term somehow came to mean a small snack eaten while sitting on a low bench, such as a meal taken on the family workbench. From there it came to mean a feast.

The word banquet is mentioned Homer’s “The Iliad” in regards to feasts. Zeus has a banquet feast with the “worthy Ethiopians” in Oceanus, and at the end of the poem, the gods have a banquet on Olympus to discuss the matter of aiding the Trojans.
The word is associated with the God Apollo, who provided the entertainment at such banquets, playing his golden lyre with his choir, The Nine Muses. This association with Olympian gods may be the source of the word being used to refer to feasts for the powerful and wealthy.