英语词源字典 - 在线词源网站

era [era 词源字典]: era: [17] In ancient Rome, small discs or tokens made of ‘brass’ (Latin aes, a descendant, like English ore [OE], of Indo-European *ajes) used for counting were known as area. In due course this developed the metaphorical meaning ‘number as a basis for calculation’, and from around the 5th century AD it came to be used in Spain, North Africa, and southern Gaul as a prefix for dates, some what analogous to modern English AD.

By extension it was then applied to a ‘system of chronological notation, as dated from a particular event or point in time’, the sense in which English acquired the word. The more general ‘historical period’ is an 18thcentury semantic development.
=> ore[era etymology, era origin, 英语词源]
disc (n.): Latinate spelling preferred in British English for most uses of disk (q.v.). American English tends to use it in the musical recording sense; originally of phonograph records, recently of compact discs. Hence, discophile "enthusiast for gramophone recordings" (1940).
phonovision: "A system of television, invented by John Logie Baird but never publicly demonstrated, whereby vision and sound signals could be recorded on discs similar to gramophone records", 1920s; earliest use found in Punch.