I was suprised to read this, and upon LIU have my doubts.

I agree, Helen. Can’t see there is a lot of discussion about it, Keiva – even the AHD refers to the word’s etymology as [Middle English, grain, from Old English.]

It may be only ”chiefly British”, but the UK has had some influence on the development of the English language, and it is the wider meaning current outside the USA which also has given us such formations as ‘cornloft’ for granary, ‘corn-law’ relating to grain imports, and even ‘corn-rig’ from Scotland meaning a strip of ground on which oats are grown.

My trusty old Chambers offers this for the noun: a grain, hard particle: a kernel, small hard seed: collectively seeds of cereal plants, or the plants themselves: esp. (in England) wheat, (in Scotland and Ireland) oats, (in N America) maize… and adds v.t. to make granular: to sprinkle with grains of salt… which adds to the etymological baggage to do with granularity.

Of course, the prevalence of Merkin Kulcha has widened the currency of the narrow meaning…

and speaking of widening, Helen PLEASE edit that post!