年代
ねんだい · nendai · JLPT N3 · noun
era
⏳📅 年代 = year + generation: a span of years, like the 1980s
年 (nen) means year and 代 (dai) means generation or reign, as in 時代 (jidai, era). Together they mean a stretch of years. 1990年代 means the 1990s.
年 — grain 禾 over person 人 (oracle bone)
Originally a pictograph of a person carrying a bundle of harvested grain on their back, representing the yearly grain harvest. Because harvests came once a year, the character shifted from meaning 'harvest' to meaning 'year.' The modern form 年 obscures the original 禾 (grain) + 人 (person) structure.
代 — person radical 亻 + 弋 (stake/dart, phonetic)
代 is a semantic-phonetic compound: 亻 (person) gives the meaning and 弋 supplies the sound. The original sense was one person taking the place of another, which broadened to 'substitute,' 'replace,' and then 'generation' or 'era' — successive groups of people replacing the previous.