The most famous journey in Western literature is named after a man whose own name nobody can explain.
Odyssey is the Greek title Odysseia, which simply means the poem of Odysseus. The poem has 24 books and follows the king of Ithaca as he tries to get home after the Trojan War. He wanders for ten years, yet the action of the poem covers only the last six weeks of that trip. Scholars date its first composition to roughly the 8th or 7th century BC, and they have never agreed on a firmer date.
The hero's name is the real puzzle. Ancient poets tied it to the Greek verb odyssasthai, "to be angry or grieved." Modern etymologists treat this as a folk etymology, a meaning invented after the fact. The linguist Beekes argued that the name is Pre-Greek, partly because it appears in so many variant forms.
Those variants explain why the Romans called him Ulysses. Some Greek forms had an l instead of a d, such as Olysseus and Oulixeus, and Latin inherited Ulixes and Ulysses from them. Etymonline notes that the Latin shift from d to l is the one linguists call the "Sabine L."
English first used odyssey around 1600, and only for Homer's poem. The word stayed a proper title for almost three centuries. By 1889 it had become a common noun for any long, wandering and eventful journey, the sense we use for road trips, career paths and a very bad commute.
That shift turned a specific hero into a general idea. Nobody needs to have read the poem to call a trip an odyssey. The word carries the shape of the story: a long way home, with delays, detours and trouble at every stop.
The poem's own name has therefore outlived its meaning in a quiet way. Nobody can say what Odysseus's name meant, but everyone knows what an odyssey is.