Dissimilar, a.
Etymology: [Pref. dis- + similar: cf. F. dissimilaire.]
Not similar; unlike; heterogeneous; as, the tempers of men are as dissimilar as their features. This part very dissimilar to any other. Boyle.
Shades of meaning
Fernald has no entry of its own for dissimilar; he lists it under heterogeneous.
He lists it without comment; the entries above explain its neighbors.