1. A movement or action that occurs without deliberate intention or conscious control
The sudden unintentional motion of his hand caused him to spill the coffee.
O movimento involuntário súbito de sua mão fez com que ele derramasse o café.
2. In physics or mechanics, motion that is not consciously or deliberately produced
The unintentional motion of the machinery was due to a mechanical defect.
O movimento involuntário da máquina foi causado por um defeito mecânico.