Fourth in an irregular series.
The average man (and typographer) on the street calls the big letters upper case and the small ones lower case. The primary schooler learning the alphabet for the first time might say big A, little A. Neither are incorrect, of course, but these usages are actually rather modern.
For the letter we call upper case, the large letter, the historical term is majuscule. It stems from the Latin maiusuclos, or rather large.
For the letter we call lower case, the small letter, the historical term is minuscule. It, similarly, stems from the Latin minusculos, or rather small.
The terms upper and lower case, as is well known, stem from the printing trade, where hand compostion of type necesstated sorting metal type into two trays for ease of location–the upper one holding the majuscules, the lower one holding the minuscules.
A famous usage of the word minuscule is to describe the calligraphic mode insipred by the Emperor Charlemagne for enhanced communication through the Frankish Empire. Made entirely of what we would term lower case letters with not a capital in sight, it has come to be known as the Carolingian Minuscule.

