cheer: [13] Originally, cheer meant ‘face’. It came via Anglo-Norman chere ‘face’ and late Latin cara ‘face’ from Greek kárā ‘head’. As often happens, ‘face’ was taken as a metaphor of the mental condition causing the expression on it, so ‘be of good cheer’ came to mean ‘be in a good mood’; and gradually cheer grew to be used on its own for ‘happy frame of mind, cheerfulness’. It first appears in the sense ‘shout of applause or encouragement’ at the start of the 18th century, when Daniel Defoe identifies it as a nautical usage. [cheer etymology, cheer origin, 英语词源]