[ adj ] occurring without motivation or provocation <adj.all> motiveless malignityunprovoked and dastardly attack
Motiveless \Mo"tive*less\, a. Destitute of a motive; not incited by a motive. -- {Mo"tive*less*ness}, n. --G. Eliot.
But what marks out today's cinema of cruelty is that the phrase has lost pejorative point in an age when films featuring brutal or sadistic events are about the excitement that characters obtain from that seemingly motiveless cruelty.