1. To foam and churn as if boiling: While Sue was cooking, she had water that was seething and bubbling in a pan where she was going to put some vegetables.
2. To be violently disturbed, against, or excited about something: Tom's children were seething with frustration when their TV wouldn't function during the storm.
3. To be very active: John's brain was seething with ideas about how to improve the contents of his writing project.

The farmer was exasperated when he saw his fields being seethed with millions of grasshoppers.

4. Etymology: from Old English seothan, "boil".