Definition of "achromatic" []

• Designating color perceived to have zero saturation and therefore no hue, such as neutral grays, white, or black. (adjective)
• Refracting light without spectral color separation. (adjective)
• Biology Difficult to stain with standard dyes. Used in reference to cells or tissues. (adjective)
• Music Having only the diatonic tones of the scale. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "This might not necessarily be a real appearance for it is conceivable that such traces of colour might be due to the telescopes employed not having been truly achromatic, that is, not sufficiently corrected for colour; but making every allowance for this possible source of mistake there yet remains proof that the colour which has often been seen has been real."
• "In a refracting telescope we have to employ what is known as the achromatic combination, consisting of one lens of flint glass and one of crown glass, adjusted to suit each other with extreme care."
• "Of course the presence of either of these defects is certainly and correctly indicated by the appearance of one or the other of the colors, under certain circumstances; but the simple visibility of prismatic color is by no means a reliable indication of over or under correction of color, and, indeed, to the honor of our opticians, it may be stated that very few objectives are made that cannot justly be called achromatic in the general sense of the term."