corn: [OE] The underlying sense of corn is of grinding down into small particles. The word comes ultimately from the Indo-European base *ger-, which meant ‘wear away’. From it was derived *grnóm ‘worn-down particle’, which in Latin produced grānum (source of English grain) and in prehistoric Germanic produced *kurnam, which developed into Old English corn.
Already in Germanic times the word had developed in meaning from simply ‘particle’ to ‘small seed’ and specifically ‘cereal grain’, but English corn was not of course applied to ‘maize’ before that plant came to Europe from America in the 16th century. The original sense ‘particle’ survives in corned beef, where corned refers to the grains of salt with which the meat is preserved.
The meaning ‘hackneyed or sentimental matter’ is a 20th-century development, based on the supposedly unsophisticated life of country areas. Kernel comes from an Old English diminutive form of corn. Corn ‘hardening of the skin’  is a completely different word, coming via Anglo- Norman corn from Latin cornū ‘horn’. => grain; horn
"grain," Old English corn, from Proto-Germanic *kurnam "small seed" (cognates: Old Frisian and Old Saxon korn "grain," Middle Dutch coren, German Korn, Old Norse korn, Gothic kaurn), from PIE root *gre-no- "grain" (cognates: Old Church Slavonic zruno "grain," Latin granum "seed," Lithuanian žirnis "pea"). 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. 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. Cornflakes first recorded 1907. Corned beef so called for the "corns" or grains of salt with which it is preserved; from verb corn "to salt" (1560s).
"hardening of skin," early 15c., from Old French corne (13c.) "horn (of an animal)," later, "corn on the foot," from Latin cornu "horn," from PIE *ker- (1) "horn; head, uppermost part of the body" (see horn (n.)).