The first time the word vegetable appeared in English was in a very early translation of a mediaeval Latin poem which took a full eight years to finish. Troy Book was one of the first books written to showcase the English language. Its author John Lydgate (a contemporary of Chaucer and a major early writer of English) commented in his prologue that the book was just as good in English as in Latin and French. He was right. His work was also a source to a later Shakespeare work Troilus and Cressida.
Vegetable in the French and Latin of the time meant being alive, being able to grow. It is used in reference to the dead Hector who was embalmed, but who looked so full of life that he was vegetable, i.e. had a soul and seemed to be alive. This idea of a vegetable soul which is alive planted in an earthly body was a common use of the word for some 200 years.
The idea of vegetable as being a food which was not alive was used for the first time in 1700. Once again it was a famous English poet who was translating from Latin. This time is was Dryden who wrote:
Nourish life with vegetable food
And shun the sacrilegious taste of blood.
Soon afterwards the word began to be used as a word to describe a plant used for food. It was a landscape gardener who introduced the word in its most common form in English. Stephen Switzer (who was also involved in the garden at Blenheim Palace) also wrote The Practical Kitchen Gardiner. There in 1727 he states that “artichokes, as most other kitchen vegetables” like deep soil. Switzer also introduced into English such phrases as garden plant, melon merchant pond maker.
From this time onwards the vegetable became a part of the culture. A vegetable garden was described in 1756, a vegetable market in 1789.