"a spot," especially a large irregular spot, as on the skin, c. 1600, perhaps an extension of blot (n.) by influence of botch or patch. Also from c. 1600 as a verb. Related: Blotched; blotching.
plural maculae, "a spot, blotch," especially on the skin or eye, c. 1400, from Latin macula "spot, stain," used of various spots (sunspots, markings on minerals, etc.), from Proto-Italic *smalto-, which is of uncertain origin. The macula lutea of the eye, the yellow spot of the retina opposite the pupil (the position of the most distinct vision), is from 1848.