To put shackles or chains on someone; to bind or restrict someone's freedom.
From Old English 'be-' (prefix meaning 'to make or cause') + 'shackle' (a metal restraint). The 'be-' prefix was commonly used in Middle English to turn nouns into verbs meaning to equip with or cover in that thing.
English had this brilliant prefix 'be-' that acted like a word-building machine—you could say 'beshade' (cover with shade), 'beshell' (put in a shell), or 'beshackle' (put in shackles). It's like adding '-ify' today, but it fell out of fashion by the 1700s, leaving these quirky archaic verbs as fossils.
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