Today’s idiom: fight tooth and nail
Meaning: putting all your effort behind something, fighting fiercely for something you believe in
Origin: Obviously this could be seen as literal, as in using your teeth and nails in fights, but it’s often used figuratively. In 1535 Sir Thomas More wrote in A Dialogue of Comfort and Tribulation about a fictional debate, where one of the characters is talking about how some men love things of this world so much that “they would faine kepe them as long as ever they might, even with tooth and naile.”
Source: the grammarphobia blog.