The word entered English in 1633, from Latin. Its earliest recorded use appears in Pacata Hibernia, a chronicle of England's war in Ireland, describing the exchange of English money for the new currency standard imposed that same year by Thomas Wentworth, Lord Deputy of Ireland.
It came directly from Latin, with no other language standing between. Bishop Jeremy Taylor, in his 1660 work Ductor Dubitantium, described a man who believed it was unlawful to exchange a vow for something else, insisting he was bound to keep his promise exactly as made.
Behind the Latin word lay two parts, a prefix that intensified the verb, and a verb meaning to change. Behind that verb lies a Proto-Indo-European root, *mei-, meaning to move. The same root gave Sanskrit a word meaning to alternate, or to change.
MOULT and MUTUAL share the same distant root. MOULT entered English around 1400, describing the shedding of feathers, fur, or skin. The letter L was added later, by analogy with other English words, though it was never part of the original spelling. MUTUAL entered English in the late fifteenth century, from French, originally describing feelings given and received in equal measure between two people.
By the seventeenth century the word had entered the courtroom. Thomas Fuller, in his 1642 work The Holy State, first used it in this sense, describing the local custom of changing a public whipping into a payment of money. In 1822 The Long-Island Star used a related term for a discounted travel document, and by 1889 the word had come to describe the journey made using one.
