Which word or phrase is not derived from the latin verb meaning "to follow"?
a. exonerate
b. nonsequitur
c. obsequious
d. sequester

The words Non sequitur, obsequious, sequester have their definition derived from the Latin word sequi which means "to follow" . 

 Non sequitur means inference that doesn't follow from premises. In Latin, it literally means "it does not follow".
Obsequious is to comply. It is from the Latin words ob meaning toward, and sequi meaning to follow.
sequester or entrust is also from the Latin word sequestrare meaning to hand over to a trustee. sequestrare is similar to the latin term sequi which means to follow. 

The word exonerate is the only word that is not related to any of the words above. Exonerate means to prove that someone is not guilty of a crime. So, the answer is exonerate, letter A..