Plead (pronounced "pled") for Pleaded. "He plead guilty."
Plenty for Plentiful. "Fish and fowl were plenty."
Poetess. A foolish word, like "authoress."
Poetry for Verse. Not all verse is poetry; not all poetry is verse. Few persons can know, or hope to know, the one from the other, but he who has the humility to doubt (if such a one there be) should say verse if the composition is metrical.
Point Blank. "He fired at him point blank." This usually is intended to mean directly, or at short range. But point blank means the point at which the line of sight is crossed downward by the trajectory—the curve described by the missile.
Poisonous for Venomous. Hemlock is poisonous, but a rattlesnake is venomous.
Politics. The word is not plural because it happens to end with s.
Possess for Have. "To possess knowledge is to possess power." Possess is lacking in naturalness and unduly emphasizes the concept of ownership.
Practically for Virtually. This error is very common. "It is practically conceded." "The decision was practically unanimous." "The panther and the cougar are practically the same animal." These and similar misapplications of the word are virtually without excuse.
Predicate for Found, or Base. "I predicate my argument on universal experience." What is predicated of something is affirmed as an attribute of it, as omnipotence is predicated of the Deity.