buff
n. countable B2 Upper Intermediate US //ˈbəf// UK //bˈʌf// buff
n. someone who is very interested in a particular subject and knows a lot about it. You use this when you want to describe a person who is an expert or a big fan of something like movies or history.
n. an enthusiast or devotee of a specific subject or activity. Informal in register; typically follows a noun that specifies the area of interest.
My brother is a huge movie buff.
As a history buff, she spent her entire vacation visiting every museum and battlefield in the region.
The director, a noted jazz buff, filled the soundtrack with rare recordings from the 1950s to create an authentic atmosphere for the film.
Usage
Typically functions as the head of a compound noun phrase, preceded by the subject of interest (e.g., 'history buff', 'film buff').