A state of curiosity or concern about or attention to something: an interest in sports. Something, such as a quality, subject, or activity, that evokes this mental state: counts the theater among his interests. Regard for one's own benefit or advantage; self-interest. Often used in the plural: It is in your best interest to cooperate. She kept her own interests in mind. A right, claim, or legal share: an interest in the new company. Something in which such a right, claim, or share is held: has interests overseas. A person or group of persons holding such a right, claim, or share: a petroleum interest. Involvement with or participation in something: She has an interest in the quality of her education. A charge for a loan, usually a percentage of the amount loaned. An excess or bonus beyond what is expected or due. An interest group. The particular cause supported by an interest group. To arouse the curiosity or hold the attention of: Your opinions interest me. To cause to become involved or concerned with: tried to interest her in taking a walk. Obsolete To concern or affect. interest To the advantage of; for the sake of: thinking in the interest of the whole family; ate breakfast on the train in the interest of time.