fierce, ferocious, barbarous, savage, cruel mean showing fury or malignity in looks or actions. fierce applies to humans and animals that inspire terror because of their wild and menacing aspect or fury in attack.
Fierce can also mean severe or extremely strong: She's a fierce critic of US policies. He was a fierce competitor.
FIERCE Synonyms: 411 Similar and Opposite Words - Merriam-Webster
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Synonyms for FIERCE: ferocious, savage, vicious, ruthless, merciless, fell, grim, brute; Antonyms of FIERCE: mild, gentle, warm, friendly, congenial, tame, ...
having a violent and unrestrained nature; savage. a fierce dog · wild or turbulent in force, action, or intensity. a fierce storm · vehement, intense, or strong.