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I think both "corn on the cob" and "an ear of corn" mean the same thing. Am I right?

Here is a picture :

Similarly, I think, "a kernel of maize" or "a grain of the maize" are same. Am I right?
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An ear of corn is a unit; corn-on-the-cob is a food preparation style, and is uncountable.

A kernel of maize is fine, but a grain of maize is odd to me. Corn and other succulent seeds (nuts, etc) normally come in kernels, while little tiny dry cereals (wheat, rice, oats) are usually referred to as 'grains'.
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Sweetcorn can refer to either the whole thing or just the kernels.
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Comments  
Thank you Mister Micawber.

I think "a kernel of maize" is called "sweetcorn". Am I right?
 nona the brit's reply was promoted to an answer.
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