Cornish \Cor"nish\ (k?r"n?sh), a. Of or pertaining to Cornwall, in England. {Cornish chough}. See {Chough}. {Cornish engine}, a single-acting pumping engine, used in mines, in Cornwall and elsewhere, and for water works. A heavy pump rod or plunger, raised by the steam, forces up the water by its weight, in descending.