The spelling appears a few different ways (“zamzod,” “zamzaw’d,” “samsawed,” “zamsod,” and a few other phonetic variations), but this bit of Devonshire slang describes food that has been dried out by overcooking it. It likely comes from the Germanic prefix “sam-” (meaning “half”) and “sod” (meaning “boiled”), but instead of meaning “half-boiled,” the usage turned into “overcooked.”