1520s, "refusal to grant what is requested or desired;" see deny + -al (2). Replaced earlier denyance (late 15c.). Sense of "act of asserting to the contrary, contradicting" is from 1570s; that of "refusal to accept or acknowledge" is from 1580s. In some 19c. uses, it really means "self-denial." Meaning "unconscious suppression of painful or embarrassing feelings" first attested 1914 in A.A. Brill's translation of Freud's "Psychopathology of Everyday Life"; hence the phrase in denial, popularized 1980s.