1550s, "the grain of Indian corn;" 1580s of the cereal plant of the grass family that produces it, from Cuban Spanish maiz, from Arawakan (Haiti) mahiz, the native name of the plant. In Europe it was formerly also called Turkey corn; like the fowl, this is from mistaken notions of its origin.
Old English polente, "a kind of barley meal," from Latin pollenta, polenta, literally "peeled barley," related to pollen "powder, fine flour" (see pollen), but the ultimate origin is uncertain. English later reborrowed it 19c. from Italian polenta (from the Latin word) for "porridge made of corn (maize)," a principal food in northern Italy, originally made from chestnut meal.
"grain," Old English corn "single seed of a cereal plant; seeds of cereal plants generally; plants which produce corn when growing in the field," from Proto-Germanic *kurnam "small seed" (source also of Old Frisian and Old Saxon korn "grain," Middle Dutch coren, German Korn, Old Norse korn, Gothic kaurn), from PIE root *gre-no- "grain."
The sense of the Old English word was "grain with the seed still in" (as in barleycorn) rather than a particular plant. Locally understood to denote the leading crop of a district. It has been restricted to the indigenous "maize" in America (c. 1600, originally Indian corn, but the adjective was dropped), usually "wheat" in England, "oats" in Scotland and Ireland, while Korn means "rye" in parts of Germany.
Maize was introduced to China by 1550, it thrived where rice did not grow well and was a significant factor in the 18th century population boom there. Corn-starch is from 1850. Corn-silk is attested from 1852.