Here’s something interesting I didn’t know until I looked it up today… the word ‘Jerkin’, which causes so much confusion in period, is the newer of the two words. I have – to this point – always operated under the assumption that they were two regional words for roughly the same thing that eventually grew to such commonplace usage that they lived on to confuse future costumers.
“Jack: A short and close-fitting upper garment of men & women; a jacket. […] Ultimate origin uncertain, but app. French: thought by some to be identical with the proper name Jacques, perhaps as originally worn by the peasantry.” First documented appearance: 1375
“Doublet: A close-fitting body-garment, with or without sleeves, worn by men from the 14th to the 18th centuries (rarely applied to a similar garment worn by women)” it goes on to say… “The doublet had many changes of fashion, being at one time with, at another time without, short skirts. In its various sleeved and sleeveless forms, it was the prototype of the modern coat, jacket and waistcoat.”
“Jerkin: A garment of the upper body worn by men in the 16th and 17th centuries; a close-fitting jacket, jersey or short coat often made of leather.” First documented appearance: 1519.
So… there you go then.
A jacket is a unisex item of utility, thought to denote a peasant garment of French extraction. The Doublet is a man’s garment, with or without sleeves. (Note that the women’s ‘Doublet’ bodice was apparently rarely referred to as such in period documents, but no citations noted.) And a Jerkin is a later appellation most often referring to a leather garment, though bandied about quite a bit to cover jerseys and just about anything else. One of the citations (from 1599 by Thynne notes: “A common garment dalye used such as we call a jerken or jacket without sleeves.” (emphasis added by me) so at least by 1599, in common parlance, the ‘jerken’ (sic) had become synonymous not with the doublet, but with the jacket as a utilitarian garment.