Définition et Signification de "a straight face"

What is the origin of the idiom "a straight face" and when to use it?

The idiom "a straight face" can be traced back to the early 19th century. It derives from the literal meaning of "straight," which refers to something that is not crooked or bent, suggesting a neutral and unexpressive appearance. The expression gained popularity in English-speaking cultures as a way to describe maintaining a neutral facial expression, especially in situations where one might normally show a smile or frown. It is used when individuals need to keep their composure or hide their true feelings, often in contexts involving humor, irony, or situations that might cause amusement.