Nebulous comes from the Latin word nebulosus, meaning "misty," which in turn comes from nebula, meaning "mist," "fog," or "cloud." In the 18th century, English speakers borrowed "nebula" and gave it a somewhat more specific meaning than the Latin version. In English, "nebula" refers to a cloud of gas or dust in deep space, or in less technical contexts, simply to a galaxy. "Nebulous" itself, when it doesn't have interstellar implications, usually means "cloudy" or "foggy" in a figurative sense. One's memory of a long-past event, for example, will often be nebulous; a teenager might give a nebulous recounting of an evening's events upon coming home; or a politician might make a campaign promise but give only a nebulous description of how he or she would fulfill it.
