Or double-ply windows.

Plying his trade upstairs.

Well, is it two-ply? Because if it's two-ply, I'll take one ply. One ply.

Re-ply the paper.

One-ply toilet paper.

No boats plying, see...?

Triple-ply quilted?

So... ply me.

One puny little ply. I'll take one measly ply!

The trade that we ply