In British English, unreliable or likely to break down; a fake shirt front worn under a jacket; also meaning faulty or in poor health.
Origin uncertain; possibly a rhyming slang derivative or from 'Dick' as a generic name. The shirt meaning dates to the 1800s when men would wear fake fronts to look formal without full shirts.
A 'dicky' shirt front is pure Victorian fashion genius—rich people wore elaborate shirt fronts with ruffles, so poorer Victorians wore fake plastic fronts that looked expensive but cost pennies, literally faking it centuries before Instagram.
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