πέμπτος

Revelation 6:9 πέμπτην fifth

And when the Lamb opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the testimony they had upheld.

Here: "Fifth". Here the pattern changes. With seals one to four a living creature called "Come!" and a horseman rode out. Now nobody calls, nothing rides out, and the scene moves from the earth to the heavenly altar.

Revelation 9:1 πέμπτος fifth

Then the fifth angel sounded his trumpet, and I saw a star that had fallen from heaven to earth, and it was given the key to the pit of the Abyss.

Here: The fifth of seven trumpets. It is also the first of the three 'woes' the eagle announced in 8:13 (see 9:12), so the series gets sharply worse from here.

Revelation 16:10 πέμπτος fifth

And the fifth angel poured out his bowl on the throne of the beast, and its kingdom was plunged into darkness, and men began to gnaw their tongues in anguish

Here: Stands for "the fifth angel". In the critical text the noun "angel" is left out because it is obvious from context. This is the fifth of seven bowls, and the series is moving toward its climax.

Revelation 21:20 πέμπτος fifth

the fifth sardonyx, the sixth carnelian, the seventh chrysolite, the eighth beryl, the ninth topaz, the tenth chrysoprase, the eleventh jacinth, and the twelfth amethyst.

Here: Ordinal number continuing the count of the twelve foundation layers started in v. 19 (first through fourth).