mini-

1580s, "a reduced image, anything represented on a greatly reduced scale," especially a painting of very small dimensions, from Italian miniatura "manuscript illumination or small picture," from past participle of miniare "to illuminate a manuscript," from Latin miniare "to paint red," from minium "red lead," used in ancient times to make red ink, a word said to be of Iberian origin. Sense development is because pictures in medieval manuscripts were small, but no doubt there was influence as well from the similar-sounding Latin words that express smallness: minor, minimus, minutus, etc.

1660s, "smallest portion into which matter is divisible," a sense now obsolete, from Latin minimum "smallest" (thing), neuter of minimus "smallest, least," superlative of minor "smaller" (from PIE root *mei- (2) "small"). Meaning "smallest amount or degree, least amount attainable" is from 1670s.