The things you learn: ounces and inches

Apparently, ounce and inch both go back to Latin uncia “one-twelfth part” (of a pound, foot, etc.).

ounce was borrowed via French while inch came directly from Latin into Old English, which accounts for the different sound changes each word went through.

So those words are doublets just like skirt/shirt, fragile/frail, and so on.

Fun stuff!