Perpendicular, which merely means at right angles to something else mentioned, should not be used for vertical.
Plenty, a noun should not be confused with the adjective plentiful.
Politics is singular.
Post does not mean inform.
Predicate should not be used in the sense of predict or in the sense of base or found.
Premature means "before the proper time." It should not be used in a general way as equivalent to false.
Pretty should not be used in the modifying sense, nor as a synonym for very in such phrases as "pretty good," "pretty near," and the like.
Preventative, no such word, say preventive.
Promise should not be used in the sense of assure.
Propose, meaning "to offer" should not be confused with purpose meaning "to intend."