achromatic lens

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A combination of lenses made of different glass, used to produce images free of chromatic aberrations.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun optics A lens generally composed of two separate lenses, one convex and one concave and generally of different materials, in such a way that the chromatic aberration produced by one is corrected by the other.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a compound lens system that forms an image free from chromatic aberration