'Tribulation' in the Bible

Yet hath he not root in himself, but dureth for a while: for when tribulation or persecution ariseth because of the word, by and by he is offended.

For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.

Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken: