According to ancient law, husbands were allowed to beat their wives with sticks that were no wider than the width of their thumb. Hence, the ‘rule of thumb’.
‘Posse’ started out as a technical term in law, part of the term ‘posse comitatus,’ which in Medieval Latin meant ‘power of the county.’
As such, it referred to a group of citizens summoned by a sheriff to preserve the public peace as allowed for by law. ‘Preserving the public peace’ so often meant hunting down a supposed criminal that ‘posse’ eventually came to mean any group organized to make a search or embark on a mission.
In even broader use it can refer to any group, period. Sometimes nowadays that group is a gang or a rock band but it can as easily be any bunch of politicians, models, architects, tourists, children, or what have you, acting in concert.
You might expect that the original pork barrels were barrels for storing pork — and you’re right. In the early 19th century, that’s exactly what ‘pork barrel’ meant.
But, the term was also used figuratively to mean ‘a supply of money’ or ‘one’s livelihood’ (a farmer, after all, could readily turn pork into cash).
When 20th-century legislators doled out appropriations that benefited their home districts, someone apparently made an association between the profit a farmer got from a barrel of pork and the benefits derived from certain state and federal projects. By 1909, ‘pork barrel’ was being used as a noun naming such government appropriations, and today the term is often used attributively in constructions such as ‘pork barrel politics’ or ‘pork barrel project.’
Lynch law (lynching) is a term describing the rough-and-ready administration of justice by a mob in cases where the law is inadequate or dilatory (nowadays popularly meaning the execution of a supposed criminal). The term originates from the practice of Charles Lynch, a farmer in Virginia, USA who during the later part of the 18th century supported revolutionary principles in the district where he lived by catching ‘Tories’ and infamous people, whom he then hanged by their thumbs until they cried out ‘Liberty for All’.