约束
yuēshù · HSK 5
restrain
⛓️ 约 = appointment/pact + 束 = bundle/tie up → a binding agreement that restrains
约 carries the sense of agreement or pact; 束 means to bundle or tie. Together they form the idea of binding someone by agreement — to constrain, restrain, or commit to limits.
约 — silk radical 糹/纟 + ladle 勺
约 combines the silk radical 糹 with 勺 (ladle), which provides the sound. Originally it referred to binding or tying with silk cords, from which came the meanings 'to bind by agreement,' hence 'pact, appointment,' and later 'approximately' (a loose, tied-up estimate).
束 — 木 (tree) with 口 wrapped around middle
Pictograph of a bundle: a tree or sticks (木) tied together with a band or rope (depicted by the enclosing 口 in the middle). The original sense was 'to bind' or 'a bundle,' which extended to meanings like 'to restrain,' 'to control,' and the measure word for bundled things.