Unlike, a.
1. Not like; dissimilar; diverse; having no resemblance; as, the cases are unlike.
2. Not likely; improbable; unlikely. [Obsoles.] Unlike quantities (Math.), quantities expressed by letters which are different or of different powers, as a, b, c, a2, a3, xn, and the like. -- Unlike signs (Math.), the signs plus (+) and minus (-).
Shades of meaning
Fernald has no entry of its own for unlike; he lists it under alien, heterogeneous.
Where he writes about it:
In their figurative use, that is foreign which is remote, unlike, or unconnected; that is alien which is conflicting, hostile, or opposed. — from alien
Substances quite unlike are heterogeneous as regards each other. — from heterogeneous