The adverb: in a way where nothing much happened, and nothing went wrong. It almost always describes how a stretch of time passed — the day passed uneventfully, the rest of the trip went uneventfully, the night passed uneventfully. In fact the verbs it goes with are few: pass, go, proceed, end, and occasionally continue. That narrow pattern is the useful thing to remember. Like the adjective, it usually carries quiet relief rather than complaint, and it is more written than spoken; in conversation you would simply say "nothing happened".