Domination of a person by an idea, thought, feeling, etc. Also occasionally: the thought or feeling itself, a preoccupation, an obsession.

An obsession, favourite subject.

In immaterial sense: Firmly attached or implanted; securely established; secured against alteration or dislodgement. In early use often (now rarely)…

A fixed idea (see fixed, adj. 2), an obsession.

a fixed idea, an obsession; a subject to which one always returns.

Psychology. In Freudian theory: the arresting of the development of a libidinal component at a pregenital stage, so that psychosexual emotions are…