ach•ro•mat•ic(ak´rəmat´ik, ā´krə-) adj.

 1 colorless; specif., designating or of the group of colors comprising black, white, and gray: opposed to chromatic ( adj. 2): see also color ( n. 3-4)
 2 refracting white light without breaking it up into its component colors
 3 forming visual images whose outline is free from prismatic colors[an achromatic lens]
 4 Biol.
 a) staining poorly with the usual stains
 b) made of achromatin
 5 Music without accidentals; diatonic[an achromatic scale]
—ach´romat´ically adv.