Longman Dictionary of Contemporary English
firefighter
fire‧fight‧er (also fire fighter) /ˈfaɪəˌfaɪtə $ ˈfaɪrˌfaɪtər/ noun [countable]
someone whose job is to stop fires burning ⇒ fireman
Oxford Advanced Learner's Dictionary
fire·fight·er [ˈfaɪəfaɪtə(r)] 
[ˈfaɪərfaɪtər] 
noun
a person whose job is to put out fires
see also fireman
Derived Word: firefighting
Example Bank:
• A wildfire near Sydney killed three firefighters.
• Firefighters battled to save a historic building after arsonists set it alight.
• Firefighters rescued a driver trapped in the wreckage of his car.
• Firefighters tackled a warehouse blaze.
• Firefighters were called to a house in Summertown.
Cambridge Advanced Learner's Dictionary
firefighter
firefighter /ˈfaɪəˌfaɪ.təʳ/ US /ˈfaɪrˌfaɪ.ţɚ/ /-mən/
noun [C]
a person whose job is to stop fires from burning
firefighting /ˈfaɪəˌfaɪ.tɪŋ/ US /ˈfaɪrˌfaɪ.ţɪŋ/
noun [U]
the activity of stopping fires burning