mid 18th century: from French, from Dutch (see manikin)
In English usage, the word mannequin occurs much more frequently than any of its relatives manakin, manikin, and mannikin. The source for all four words is the Middle Dutch mannekijn (modern Dutch manneken) ‘little man,’ ‘little doll.’ Mannequin is the French spelling from this Dutch source. One of its French meanings, dating from about 1830, is ‘a young woman hired to model clothes’ (even though the word means ‘little man’). This sense—still current, but rare in English—first appeared in 1902. The far more common sense of ‘a life-size jointed figure or dummy used for displaying clothes’ is first recorded in 1939. Manikin has had the sense ‘little man’ (often contemptuous) since the mid 16th century, when it was sometimes spelled manakin (as it appeared in Shakespeare’s Twelfth Night, as a term of abuse). Manikin’s sense of ‘an artist’s lay figure’ also dates from the mid 16th century (first recorded with the Dutch spelling manneken).To confuse matters further, in modern usage, the words manakin and mannikin refer to birds of two unrelated families. The history of these bird names is somewhat obscure. Manakin may have come from the Portuguese manaquim ‘mannikin,’ a variant of manequim ‘mannequin.’ Mannikin may have come directly from the source of the Portuguese words, the Middle Dutch mannekijn.