预订
yù dìng · HSK 4
to book ahead
📅 预订 = 预 (in advance) + 订 (set/book) — book in advance
预 means 'beforehand' (also in 预习 to preview, 预报 to forecast). 订 means 'to settle, to book' (also in 订单 order, 订婚 engagement). Together they mean to reserve or book ahead — a table, ticket, or hotel room.
订 — speech radical 讠 + nail 丁
订 combines the speech radical 讠 (word) with 丁 (nail), which also hints at the sound. The idea is words 'nailed down' into an agreement, giving meanings like to settle, arrange, subscribe, or book. 丁 is mainly phonetic here but reinforces the sense of fixing something firmly.