Definition & Meaning of "all mouth (and no trousers|)"

What is the origin of the idiom "all mouth" and when to use it?

The idiom "all mouth" originated in the early 19th century and is used to describe someone who talks boastfully or confidently about their abilities or intentions but fails to take action or deliver on their promises. The term "mouth" refers to the act of speaking or making verbal claims, while "all" emphasizes the excessive or exaggerated nature of their words. This phrase exists to suggest that the individual lacks substance or fails to back up their words with corresponding actions, often indicating a tendency towards empty bravado.