1640s, "characterized by or appropriate to dismissal;" from dismiss + -ive. Meaning "contemptuous, tending to reject as insignificant" is recorded by 1922 (implied in dismissively). Related: Dismissiveness.
`chronic fatigue syndrome' was known by the dismissive term `housewife syndrome'
a dismissive shrug
the firm is dismissive of the competitor's product
they took dismissive action after the third violation