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china (1) f. (Noun) "pebble;" "doubt"

Very late 15th cent. The meaning of doubt is a poetic metaphor. Of unknown origin, presumably from a pre-form *cina. Perhaps a back formation in Vulgar Latin from Latin cinnabris "red mercuric sulfide," but the semantics are obscure and do little to help the theory.

Chin is an apocopated form.

Romance: Western Vulgar Latin: Asturian china, Portuguese china, Galician china