1. preposition
a) Differently from.
b) In contrast with.
2. adjective
a) Not like; dissimilar; diverse; having no resemblance.
The brothers are quite unlike each other.
b) Unequal.
They contributed in unlike amounts.
3. verb
a) To dislike.
I unliked the video link after I realized it was making fun of me.
b) To withdraw support for a particular thing, especially on social networking websites
Facebook, for instance, allows you to register approval for a posted message in a very concrete way, by clicking a thumbs-up like button. Toggling off the button results in unliking your previously liked item. Note that this is different from disliking something, since unliking simply returns you to a neutral state.
Wikipedia foundation.