humble pie: [17] Until the 19th century, humble pie was simply a pie made from the internal organs of a deer or other animal (‘Mrs Turner did bring us an umble pie hot out of her oven’, Samuel Pepys, Diary 8 July 1663). Humble has no etymological connection with the adjective humble ‘meek’; it is an alteration of the now extinct numbles ‘offal’ [14] (which came ultimately from Latin lumulus, a diminutive of lumbus ‘loin’, from which English gets loin and lumbar). Numbles became umbles (perhaps from misanalysis of a numble as an umble in contexts such as numble pie), and from there it was a short step to humble; but the expression eat humble pie is not recorded in the sense ‘be humiliated’ until the 1830s.
It combines the notion of ‘food fit only for those of lowly status’ with a fortuitous resemblance to the adjective humble. => loin, lumbar
