Of an action, esp. an attack: carried out or occurring without provocation; lacking cause or motive.

= automatic, adj. (in various senses). Now rare.

Of action, etc.: self-generated, spontaneous; (of a thing) self-acting; having the power of motion within itself. In later use (Physiology): having…

Of a person or thing: that acts independently, without external cause or assistance. Of motion, a process, etc.: characterized by or involving…

Capable of or exhibiting independent action, without external cause or influence.

Of an action, deed, etc.: carried out or performed of a person's own accord or by a person's own hand. Of a person: moved to action of his or her own…

Of natural processes: Occurring without apparent external cause; having a self-contained cause or origin.

Of motion: self-generated, automatic. Obsolete. rare.

Partially automatic; spec. designating a system, device, or machine whose function is not completely automatic.

Impulsive, intuitive; hasty; frank; unplanned, spontaneous. Cf. to shoot from the hip at shoot, v. additions.