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.
"on a small scale, much reduced from natural size," 1714, from miniature (n.). Of dog breeds, from 1889. Of golf played on a miniature course, from 1893.