era

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A period of time as reckoned from a specific date serving as the basis of its chronological system.
2. n. A period of time characterized by particular circumstances, events, or personages: the Colonial era of U.S. history; the Reagan era.
3. n. A point that marks the beginning of such a period of time. See Synonyms at period.
4. n. The longest division of geologic time, made up of one or more periods.

Century Dictionary and Cyclopedia

1. n. A tale or count of years from a fixed epoch; a period during which, in some part or parts of the world, years are numbered and dates are reckoned from a particular point of time in the past, generally determined by some historical event. See phrases below.
2. n. A series of years having some distinctive historical character: as, the era of good feeling (see below).
3. n. Loosely, an epoch from which time is reckoned, or a point of time noted for some event or occurrence; an epoch in general: as, the era of Christ's appearance.
4. n. A Cæsarean era beginning 48 b. c., Oct. 1st.
5. n. An era coinciding with the reformed era of Alexandria.
6. n. In geology, a division of geologic time which, according to the recommendation of the International Congress of Geologists, is to be regarded as of highest rank, corresponding to the stratigraphic term group. See group, 3 .

Wiktionary

1. n. A time period of indeterminate length, generally more than one year.
2. n. geology A unit of time, smaller than aeons and greater than periods.

GNU Webster's 1913

1. n. A fixed point of time, usually an epoch, from which a series of years is reckoned.
2. n. A period of time reckoned from some particular date or epoch; a succession of years dating from some important event
3. n. A period of time in which a new order of things prevails; a signal stage of history; an epoch.

WordNet 3.0

1. n. a major division of geological time; an era is usually divided into two or more periods
2. n. a period marked by distinctive character or reckoned from a fixed point or event
3. n. (baseball) a measure of a pitcher's effectiveness; calculated as the average number of earned runs allowed by the pitcher for every nine innings pitched