A friend asked me a while back to talk about yoke vs. yolk, as she had seen them misused somewhere.

This is a yolk:

Egg yolk. (Yahoo Images)

A yolk is the yellow part of the inside of an egg. Less commonly, it is the natural grease exuded from the skin of sheep.

A yoke, however, is quite different:

Two oxen attached by a yoke. (Yahoo Images)

A yoke is the device shown above that attaches two animals so that they work as a team. There is also a version for humans to carry something, such as two buckets of water.

Yoke can also be used to express oppression or subjection, as in throwing off the yoke of servitude.