ultrablack adjective 1noun 1forms 3 adjective1 •Having the property of disappearing (not returning) more than 99.5% of the light incident upon it, in the specified spectral range; in the visible light spectrum. noun1 •A substance that emits (reflects) less than 0.5% of the light incident upon it, in the specified spectral range; in the visible light spectrum. formsultrablacks · more ultrablack · most ultrablack