PERUSE

Peruse: Some words lose their original meaning while others become so twisted that they end up meaning the opposite what they actually mean.

This victim of definition reversal, peruse, means "to use thoroughly," and its first sense is that of careful steady or attentive reading. However, since so many writers have employed it as a synonym for scan, its second sense is now "to look over or through in a casual or cursory manner."

Disinterested

Disinterested: This word is most commonly used to mean that someone is not interested or has no energy for something, but it actually means “neutral and unbiased.” 

So, for example, having a jury that is disinterested in the trial is not a bad thing.

Fulsome

Fulsome: This term originally meant “abundant, generous, full” and it is still used in that form. However, the meaning of this word has changed to mean “excessive, effusive.”  A fulsome society was considered a good thing, but now it could suggest an excessive and corrupt one. However, some have argued that the word is enjoying a renaissance and should be used again in its positive sense. Decide what you will but be aware of the possibility for misinterpretation.