an axe to grind
The phrase "an axe to grind" refers to a hidden personal motive or a strongly held opinion, typically based on self-interest or a personal vendetta. It implies that someone has a hidden agenda or a particular bias influencing their actions or beliefs. The phrase originates from the practice of sharpening an axe, where one would need a grindstone, symbolizing a personal interest that needs to be satisfied.
English is confusing! Why do people say "Pardon my French" when they are speaking English? Because of idioms!
An idiom is a phrase or expression that usually presents a figurative, non-literal meaning attached to the phrase. Does that sound fun? It can be!
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