de-

[[t]di͟ː-[/t]]

1) PREFIX De- is added to a verb in order to change the meaning of the verb to its opposite.

The jury may have become desensitized to the video and its brutality after seeing it dozens of times...

The need to cleanse herself, to somehow decontaminate her body was compulsive.

2) PREFIX De- is added to a noun in order to make it a verb referring to the removal of the thing described by the noun.

I've defrosted the freezer...

The fires are likely to permanently deforest the land.