Good question: they can sometimes be used interchangeably. In daily American usage, both mean the end of a process IN TIME, but ultimately has an additional meaning of AT THE MOST BASIC LEVEL. In speech, eventually tends refers only to time and is softer; ultimately is harsher. A child in the back seat of a car asks his mother: "When will we get there?" She wearily replies: "Eventually." Meaning: "We will arrive at some time in the future." (Now go back to your video games and leave mommy alone.) Tame Impala sings "We break up now, but you and I will be happier - eventually (in unspecified time)." Ultimately is trickier. In my mind, it's tied to the words "ultimate" (best or final) and "ultimatum" (a final demand with consequences). "Ultimately, you have to repay me the money, or I'm calling the police." If my boss says "Eventually, we have to figure this out," I think "Okay, at least we've got some time." If she says "Ultimately, we have to figure this out," I think, "Shit, there will be consequences if we don't." What's implied in her second statement is OR ELSE. Hope this helps.