Contrary to rule, accepted order, or general practice: irregular hiring practices. Not conforming to legality, moral law, or social convention: an irregular marriage. Not straight, uniform, or symmetrical: irregular facial features. Of uneven rate, occurrence, or duration: an irregular heartbeat. Deviating from a type; atypical. Botany Having differing floral parts, as of a zygomorphic or asymmetrical flower. Falling below the manufacturer's standard or usual specifications; imperfect. Grammar Departing from the usual pattern of inflection, derivation, or word formation, as the present forms of the verb be or the plural noun children. Not belonging to a permanent, organized military force: irregular troops. One, such as an item of merchandise, that is irregular. A soldier, such as a guerrilla, who is not a member of a regular military force.