Eddish is a farmer's word, once in general dialect use in Ireland, England and Scotland, and also written eddis and eddas in Ireland.
It is also found in the form addish in Yorkshire, ettidge in Lincolnshire and heddige in Lancashire. It means the aftermath or second crop of grass, clover, etc. Verney, a native of Derbyshire, in his engaging Stone Edge, published in 1868, has, "The hay has just been carried, and the bright green of the eddish was fair to look on." An advertisement in the Gainsburg News (Lincolnshire) of July 6th, 1867, ran, "Twenty one acres of eddish to be stocked with beast and sheep, until the 13th day of November next." The word is found in parts
of Antrim and Down to this day. Hence eddish cheese, much favoured for its particular richness, and made of the milk of cows fed
on eddish, and eddish hay, hay made of the aftergrass or eddish.

Worlidge's Rustic Dictionary of 1681 has this: "Eddish, eadish, etch, erch, the latter pasture or grass that comes after mowing or reaping." Another word for the aftermath or second crop of grass after the hay-crop is edgrow, also found in forms eddgrew, edgrew, edgrow, etgro in various parts of Lancashire, Cheshire and Shropshire to the present day. Edgrew was considered by an English Dialect Dictionary correspondent to be the most common word in use; "eddish is rare, and considered as refined." He adds, "Them key [cows] keep'n raungin' o'er the hedge after my bit o' edgrew."

The word is found in Promptorium Parvulorum Sive Clericorum, an Anglo-Latin lexicon of c. 1440, as edgrow. Compare the Old English edgrówung, a re-growing.

Another word for aftermath or after-grass is ee-grass, found in Lancashire, Gloucestershire, Hampshire and in England's West Country. Horae Subsecivae of 1777 says that the word means "old grass that has been long upon the ground without being eaten by the cattle, or grass of long standing". Also known in places as Lammas Grass. That fine Dorset dialect poet and important lexicographer, Barnes, wrote
in a poem published in 1869, "When the mowen is over, an' ee-grass do whiten wi' clover." Worlidge's Dictionarium Rusticum
of 1681 has, "Eddish or ee-grass, the latter pasture."

The word is an old one and comes from Old English edisc, pasture. For the element ed compare the Middle Dutch -ed (et-) in etgras, the aftermath; the Dutch etgroen, “the latter hay” according to Hexham’s Dutch-English dictionary of 1658. Note also the Holstein dialect ettgröde, aftergrass.