Definitions of fierce:

• adjective:   marked by extreme intensity of emotions or convictions; inclined to react violently; fervid

  Example: "Fierce loyalty"

• adjective:   ruthless in competition
• adjective:   marked by extreme and violent energy

  Example: "Fierce fighting"

• adjective:   violently agitated and turbulent

  Example: "The fierce thunders roar me their music- Ezra Pound"