wonk 
/ˈwɑ:ŋk/ noun
plural wonks /ˈwɑ:ŋk/ noun [count] US, informal + sometimes disapproving : a person who knows a lot about the details of a particular field (such as politics) and often talks a lot about that subject
▪ the policy wonks in the government
▪ the policy wonks in the government
