(ME chiete, ME-15 chet, chete, 15 chett, 15-16 cheate, cheat, (17-18 Hist. cheat, chete) also cheat-bread, cheat-loaf)
Bread made from the second quality of flour, inferior to Manchet. (OED).
Known at least since the 'The Boke of Curtasye' of 1450; "Manchet and chet bred he shalle take"
If you ordered finest manchet, but were given inferior bread, you had been cheated - it seems to be the case that the verb meaning "to substitute by trickery, to deprive, to deceive" is derived from the name of the bread. There is some indication that Sly Cake has also been refererd to as 'Cheat'.