Oatmeal

google

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late Middle English: from oat and meal2.

wiktionary

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From Middle English otemele, from ote(“oat”) + mele(“meal, coarse-ground grains”).

etymonline

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oatmeal (n.)

"the coarsely ground meal of oats," late 14c., ote-mele, from oat + Middle English mele (see meal (n.2)).