fierce
adjective /fɪəs/
  /fɪrs/
(comparative fiercer, superlative fiercest)
Idioms - (especially of people or animals) angry and aggressive in a way that is frightening- a fierce dog
- Two fierce eyes glared at them.
- He suddenly looked fierce.
- She spoke in a fierce whisper.
- The more she struggled, the fiercer he became.
 
- (especially of actions or emotions) showing strong feelings or a lot of activity, often in a way that is violent- fierce loyalty
- the scene of fierce fighting
- He launched a fierce attack on the Democrats.
- Competition from abroad became fiercer in the 1990s.
- His wife is his fiercest critic.
- The bill was passed despite fierce opposition.
 
- (of weather conditions or temperatures) very strong in a way that could cause damage- fierce wind
- the fierce heat of the flames
 
Word OriginMiddle English: from Old French fiers ‘fierce, brave, proud’, from Latin ferus ‘untamed’.
Idioms 
something fierce 
- (North American English, informal) very much; more than usual- I sure do miss you something fierce!