長期
ちょうき · chouki · JLPT N3 · na-adj
long time period
⏳📅 長期 = long (長) + period (期): a long stretch of time
長 (chou) means long, as in 長い nagai. 期 (ki) means period or term, as in 期間 kikan. Together they make a long-term period, as in 長期休暇, a long vacation. Sound hook: chou-ki, a long CHOO-choo train trip takes a KEY chunk of time.
期 — 其 (phonetic) + 月 (moon/time)
期 is a phono-semantic compound. The right side 月 (moon) signals meaning, since lunar cycles marked fixed time periods in ancient China. The left side 其 supplies the sound. Together it points to a set time, period, or appointed date — meanings still carried today in words like 期间 and 日期.