I was reading the following verse, from John, and I came across the phrase ζωὴν αἰώνιον. This phrase looks odd to me, since ζωὴν is feminine, and at first glance, αἰώνιον would seem to be masculine or neuter.
The phrase means "eternal life", and of course it's an important phrase in John (and the Gospels in general) so I wanted to become more familiar with the adjective αἰώνιον, and to know why it's inflected in such a surprising way.
Why does it have the -ον ending? I would expect, instead, to see αἰωνίαν, so that the adjective would more clearly match the gender of the noun.
ὁ πιστεύων εἰς τὸν υἱὸν ἔχει ζωὴν αἰώνιον· ὁ δὲ ἀπειθῶν τῷ υἱῷ οὐκ ὄψεται ζωήν, ἀλλ’ ἡ ὀργὴ τοῦ θεοῦ μένει ἐπ’ αὐτόν.
He who believes in the Son has eternal life. He who disobeys the Son shall not see life, but the wrath of God remains upon him.