For describing letters, what word is to “capital” as “lower-case” is to “upper-case”?
I am looking for an adjective which is a synonym of “lower-case”.
I think you are looking for non-capital or minuscule.
When talking about letter case, there are majuscule letters (depending of the context they can be capital, caps, upper-case, etc) and minuscule letters (non-capital, lower-case)
minuscule (adj.) of or in lowercase letters, as distinct from capitals or uncials.
This might sound a little too simple or silly, but in explaining to kids, we'll just use the word 'small'.
"Kids, write the 'T' as capital and the rest of the word in small letters."
Wikipedia says: "upper case (also uppercase, capital letters, capitals, caps, large letters, or more formally majuscule) and smaller lower case (also lowercase, small letters, or more formally minuscule)"