What is "gyre" in "The Second Coming"?

I have moved this question to this group, as the reference
to the word "gyre" obviously refers to this famous poem by W. B. Yeats and its first
line. The poem concerns the poet's prediction of the grim future that awaits humanity,
and the first startling image that is used to introduce this theme uses the word "gyre"
to indicate the way that culture is disintegrating. Consider the following
lines:

Turnign
and turning in the widening gyre

The falcon cannot hear the
falconer;

We are presented
therefore with the somewhat mysterious image of a falcon going round and round in an
ever widening "gyre," or a radiating spiral, moving further and further away beyond the
reach of its falconer. Of course, the further that the falcon moves away from its
falconer, the harder it is for the falconer to regain control over the bird and the
falcon cannot be diverted or controlled in its direction. The word "gyre" therefore
refers to the spiral motion of the falcon as it flies.