What do you call non-capital letters?

Answer 1

The correct term is "minuscule," but people will look at you REAL strange if you use it.

You'll like this: how "lower case" letters got their name was from hand-set typography. In hand-set work, you used blocks with letters molded into the end of them. The capital letters went into one type case, the minuscules went into another. To make it easy to work with, you put the two cases one above the other. The one with the capital letters was the upper case, and the one with the minuscules was the lower case.

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A lower-case letter, a "small letter" or a non-capital letter.