What is the meaning of seething?

verb

• Be noisy with activity.
  • usage: "This office is buzzing with activity"
  • synonyms: hum, buzz, seethe
• Be in an agitated emotional state.
  • usage: "The customer was seething with anger"
  • synonyms: seethe, boil
• Foam as if boiling.
  • usage: "a seething liquid"
  • synonyms: seethe
• Boil vigorously.
  • usage: "The liquid was seething"; "The water rolled"
  • synonyms: seethe, roll

adjective

• In constant agitation. "a seething flag-waving crowd filled the streets"; "a seething mass of maggots"; "lovers and madmen have such seething brains- Shakespeare