S: (n) eon, aeon (the longest division of geological time)
S: (n) period, geological period (a unit of geological time during which a system of rocks formed) "ganoid fishes swarmed during the earlier geological periods"
S: (n) era, geological era (a major division of geological time; an era is usually divided into two or more periods)
S: (n) epoch (a unit of geological time that is a subdivision of a period and is itself divided into ages)
S: (n) time (the continuum of experience in which events pass from the future through the present to the past) "he waited for along time"; "it took some time before he got an answer"; "time flies like an arrow"