From Longman Dictionary of Contemporary Englishpyromaniacpy‧ro‧ma‧ni‧ac /ˌpaɪrəʊˈmeɪniæk $ -rə-/ noun [countable] medicalMP someone who suffers from a mental illness that gives them a strong desire to start fires —pyromania noun [uncountable]
Examples from the Corpus
pyromaniac• A pyromaniac doesn't throw away the last three matches. 