Medical Definition of achromatic
1: refracting light without dispersing it into its constituent colors : giving images practically free from extraneous colors <an achromatic telescope>
2: not readily colored by the usual staining agents
3: possessing or involving no hue : being or involving only black, gray, or white <achromatic visual sensations> <achromatic light stimuli>
Seen and Heard
What made you want to look up achromatic? Please tell us where you read or heard it (including the quote, if possible).