<p><strong>Noun</strong></p><ul><li>a person who questions the validity or authenticity of something purporting to be factual.</li><li>a person who maintains a doubting attitude, as toward values, plans, statements, or the character of others.</li><li>a person who doubts the truth of a religion, especially Christianity, or of important elements of it.</li><li>Synonyms: doubter</li><li>Antonyms: believer</li><li>(initial capital letter) Philosophy: a member of a philosophical school of ancient Greece, the earliest group of which consisted of Pyrrho and his followers, who maintained that real knowledge of things is impossible.</li><li>any later thinker who doubts or questions the possibility of real knowledge of any kind.</li></ul><p><strong>Adjective</strong></p><ul><li>pertaining to skeptics or skepticism; skeptical.</li><li>(initial capital letter) pertaining to the Skeptics.</li></ul>