Miniscule appeared later, and is regarded by some as an error, and others as a variant. If you use minuscule, no-one will be bothered, but if you write miniscule, some people will think it is a mistake.
As a point of note, there is absolutely nothing wrong with miniscule, and it might even be preferred to distinguish "small size" from "lower case letter," which OED gives as the primary definition for minuscule (upper-case being majuscule). "Extremely small" for minuscule is definition B2 in the 2002 OED.
You can say that a is minuscule: minuscule adjective \ ˈmi-nəs-ˌkyül\ 2 : very small // minuscule amounts from m-w.com As you can see from the definition, however, "very small" is also a reasonable way to describe your thing. (Note that it is often misspelled as "miniscule", probably on the presumption that it has mini- as a prefix driving the meaning of "small", but it is in fact derived ...
The word minuscule is often misspelled as miniscule, on analogy from the derived prefix mini-, meaning small. But mini- comes from miniature, which comes from Italian miniatura, which refers to the art of illuminating a manuscript with colored inks.
How do I know when to use Jon and I, or Jon and me? I can't really figure it out. I've tried to teach myself, but I just can't seem to do it. Will someone please help me figure this problem out?
grammar - Jon and I or Jon and me? - English Language & Usage Stack ...
From this, I would tentatively conclude that (1.) the vernacular pronunciation of the name became a single-syllable "Jon" fairly early on, and (2.) the John spelling might have originally been a Latin-language abbreviation, but it came to be used as the standard vernacular spelling because it matched the vernacular pronunciation.