1) Any heating device but particularly a piece of iron which is made hot and placed in a box iron or smoothing iron.
1642 for mending the heaters in the laundry, Thornhill
1658 a smothing iron, 4 heeters, Barley
1708 one heator, a paire of cards, Pontefract. Some triangular fields were given the name Heater in this period.