1.Definition: devoid of intelligence or thought

Related Adjective(s):vacuous

2.Definition: lacking the thinking capacity characteristic of a conscious being

"The shrieking of the mindless wind"

3.Definition: not marked by the use of reason

"Mindless violence"

Related Adjective(s):reasonless, senseless

4.Definition: not mindful or attentive

Related Adjective(s):forgetful, unmindful

5.Definition: requiring little mental effort

"Mindless tasks"