mindless
Word family
Synonym discussion
Sense: adjective/1
All four words describe actions that lack good reason, but they differ in focus and intensity. Senseless is the closest synonym to mindless and is often interchangeable — a senseless killing and a mindless killing mean the same thing. Pointless shifts the focus from thought to purpose: a pointless argument may be carefully reasoned but still achieve nothing. Gratuitous is more formal and is used almost exclusively for violence, cruelty, or sexual content that is unnecessary and excessive. Thoughtless is the mildest of the group — it describes everyday inconsiderate behavior (a thoughtless comment) rather than destruction or violence. For example, kicking a stranger's car for no reason is mindless or senseless violence, but forgetting a friend's birthday is merely thoughtless.
Etymology
Mindless comes from Old English gemyndleas, formed from mind (the part of you that thinks, feels, and remembers) and the suffix -less (meaning 'without'). The word has always carried the sense of acting without thought or intelligence, dating back over a thousand years.