Explanation:
Minuscule is the preferred spelling.

Minuscule is derived from minus and not related to miniature.

Up until the last couple of decades, miniscule was usually listed as an erroneous variant but many current dictionaries simply list it as a variant. Most style guides, however, call for minuscule — so stick with that spelling.

On the Spelling Reform website, Cornell Kimball argues for removing the stigma from miniscule:

“Our own view is that any spelling which occurs so commonly, year after year, in perfectly reputable and carefully edited books and periodicals must be regarded as a standard variant.”

Let’s try an Internet spelling test.

A quick Google poll turns up:
minuscule: 3,290,000 hits
miniscule: 1,400,000 hits

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