Deadpan and Long-faced

Deadpan adjective - Not expressing any emotion.

Long-faced and deadpan are semantically related In some cases you can use "Long-faced" instead an adjective "Deadpan".

Long-faced adjective - Having a face longer than the usual.

Deadpan and long-faced are semantically related in serious topic. Sometimes you can use "Deadpan" instead an adjective phrase "Long-faced", if it concerns topics such as somber.