Woo-woo (or woo) are ideas considered irrational or based on extremely flimsy evidence or that must appeal to mysterious forces or powers. - adj. concerned with emotions, mysticism or spiritualism; rather than the rational or scientific; mysterious; new age. Also noun., a person who has mystical or new age beliefs. Derogatory and dismissive term referring to beliefs considered nonsense or to a person who holds such beliefs. Synonym for pseudoscience, true-believer or quackery.