He didn't sound very enthusiastic about the project during the meeting.

enthusiastic 是形容词，由名词 enthusiasm（热情）加上形容词后缀 -astic 构成，表示"热情的、热心的"。这个词来自希腊语 enthousiasmos，原意是"被神附体"，后来引申为"充满激情"的意思。