'To hurt,' as mentioned in Revelation 6:6, signifies violation and profanation.

In Revelation 9:4, this signifies perverting the truths and goods of the church by crafty rationalizations from sensory scientific facts and fallacies.

'To be hurt of the second death,' as mentioned in Revelation 2:11, signifies sinking under evils and falsities from hell.

(Reference: Apocalypse Explained 9 [4]; Apocalypse Revealed 316)