What makes a hymn a hymn?

The traditional view taught in most Christian music/worship classes is:
A hymn is a christian lyric or song that has no repetitious refrain. (it has no chorus sung at the end of each verse.)
A Christian Song is a collection of multiple related Christian lyrics or verses which have a refrain (a chorus) that ties them all together an is repeated after each lyric/verse.
Examples of Hymns:
And Can It Be
How Firm a Foundation
A Mighty Fortress is Our God
Holy, Holy, Holy, Lord God Almighty
O God, Our Help in Ages Past
Amazing Grace
Joy to the World (and many Christmas hymns/songs you know well)
Examples of Christian Songs:
Victory In Jesus
How Great Thou Art!
The Comforter Has Come
Jesus Paid It All
When We All Get to Heaven
Tis' So Sweet to Trust in Jesus