I have a lot of friends who are really enthusiastic about cycling, and we often go cycling together.

enthusiastic 是由名词 enthusiasm（热情）加上形容词后缀 -tic 构成的形容词，表示"充满热情的、热心的"。这个词来自希腊语 enthousiastikos，原意是"被神附体的"，后来引申为"充满激情的"。