1.
De- is added to a verb in order to change the meaning of the verb to its opposite.
...becoming desensitized to the harmful consequences of violence.
...how to decontaminate industrial waste sites.
PREFIX
2.
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.
PREFIX