chronicle, account, narrative, history, annals, geologic period
紀 centers on recording events in an ordered way: a chronicle, history, or narrative account. The geologic period sense extends this idea to a named span of time in Earth's history.
紀 combines 糸 (thread) with 己, which likely contributes the sound. The thread component suggests binding or ordering, fitting the idea of arranging events into a chronicle.
The left side 糸 is thread, and the right side 己 looks like a spool. Imagine using thread to bind pages of a chronicle together, recording history in order.
For キ, picture a key chronicle that unlocks the history of a period: key -> キ, and the thread-bound book holds the key narrative.
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century
period
pre-era; BC; BCE
traveller's journal; traveler's journal; travelogue
public morals; discipline; rules governing social behavior
this century
Nihon Shoki (second oldest work of Japanese history, compiled in 720 CE); Nihongi; Chronicles of Japan
Kii (former province located in present-day Wakayama and southern Mie prefectures)
quarter of a century
era
Kinokuniya
bulletin; memoirs
the Kojiki and Nihon Shoki (earliest historical records of Japan)
Jurassic (period)
Imperial era; system of counting years from the start of Emperor Jimmu's reign in 660 BCE
Kisei Main Line (Wakayama-Mie railway)
law and order; (official) discipline
biography
Empire Day (February 11th; national holiday held from 1872 to 1948)
millennium