When reconstructing Proto-Indo-European lexicons, scholars often debate whether a given noun should be treated as an o-stem.

In our morphology class, we compared the o-stems of several Indo-European languages.

We replaced the worn O-rings to stop the leak in the hydraulic pump.

Please replace the worn O-ring before reassembling the pump.

On our midnight walk through the marsh, we saw will o' the wisps dancing over the reeds, and for a moment the world seemed enchanted.

She wore an O-shaped pendant that gleamed in the sunlight.

The startup's demo included a prototype of the coffee-o-matic, a gadget that promised to brew and pour a perfect cup with no human input.

Students were thrilled to find O marks beside many of their answers.

When grading homework, she circled the correct answers with an O mark.

She tried to hide her o-face, but it was obvious to him.