From The Collaborative International Dictionary of English v.0.48 [gcide]:
Achromatism \A*chro"ma*tism\, n. [Cf. F. achromatisme.]
The state or quality of being achromatic; as, the achromatism
of a lens; achromaticity. --Nichol.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
achromatism
n 1: the visual property of being without chromatic color [syn:
colorlessness, colourlessness, achromatism,
achromaticity] [ant: color, coloring, colour,
colouring]