BENIGN

BENIGN     /bɪˈnʌɪn/ :        Not harmful, kind

Memory key

In our childhood most of us already might have heard malign means bad. Malign opposite word is Benign. 

A benign tomour is one which is not harmful.
A malign tomour is harmful.

It came from same root like word like benefit or beneficial is formed.

Benign animal = Not harmful

Example

Rosy have a benign personality.