Other forms: agos
Use ago to mean "earlier" or "in the past." Dinosaurs lived a long time ago.
The adverb ago refers to a time before the present moment, sometimes in the distant past, and sometimes more recently: "She just left for her appointment ten minutes ago." When you talk about the more remote past, you might say "long ago" or "a long time ago." Ago was originally a shortened form of agone in Middle English, "departed or passed away."