na-adjective, noun
irregular; undisciplined; disorganized
Describes a lack of regularity, discipline, or order in behavior, habits, or systems. Often used for lifestyle, work, or schedule.
不規律な生活は健康に悪い。
An irregular lifestyle is bad for your health.
彼の仕事のやり方は不規律だ。
His way of working is disorganized.
だらしない is a more casual, everyday word for 'sloppy' or 'undisciplined' in appearance or behavior. 不規律 is more formal and often used in written contexts.
Compound of 不 (fu, 'not') and 規律 (kiritsu, 'discipline, order'). The exact historical derivation is uncertain, but the meaning follows directly from its components.