/bɪl/
[noun] A written list of things to be paid for, or a proposed law presented to a government; also the flat part of a bird's mouth, or a type of curved cutting tool.
The restaurant bill and the duck's bill are actually two completely different words that just happen to sound the same.
The word 'bill' is not one word but several, each with its own remarkable history — they are what linguists call homonyms, words that look and sound alike but come from entirely different roots. Understanding 'bill' means untangling at least three separate threads of linguistic history, each pulling in a different direction across time.
The oldest 'bill' is the one that belongs to birds. This comes from Old English 'bile', meaning the beak or mouthpart of a bird. It is a native Germanic word, related to the Old English word 'bill' meaning a sword or cutting blade — suggesting that our distant ancestors saw the sharp beak of a bird and thought immediately of a weapon. This same root gave rise to 'billhook', the curved chopping tool still used in hedgerow management, and it connects to Old High German 'bil', meaning a pickaxe or cutting edge. The image running through all these words is one of sharpness, of something that cuts or pecks.
The 'bill' that means a document, a list of charges, or a proposed law has a very different origin. It travels through Medieval Latin 'bulla', meaning a sealed document or a round seal stamped onto official papers — the physical lump of wax that authenticated a letter. From Medieval Latin 'bulla', the word moved into Anglo-Norman and Old French as 'bulle', still meaning an official document or papal decree. From Anglo-Norman 'bulle', it entered Middle English as 'bille' in the 14th century, where it quickly broadened to mean any formal written document, notice, or list. The word 'bull' as in a papal bull shares this exact same root — both the pope's decree and your restaurant receipt are linguistic cousins.
From meaning a formal document, 'bill' gradually slipped into everyday commercial life. By the 15th century it was used for written accounts of money owed. By the 17th century, merchants were handing customers 'bills' after a transaction, and the sense of a demand for payment was firmly established. In American English, 'bill' also came to mean a banknote — a piece of paper money — following naturally from the idea of an official written document that carries monetary value. The 'bill' as a proposed law, used prominently in phrases like 'Bill of Rights', comes from the same documentary tradition: it is literally a written proposal laid before Parliament or Congress.
There is also a third 'bill', now rather old-fashioned, which was a type of long-handled weapon used in medieval warfare — a pole with a curved blade on the end, sometimes called a halberd. This comes directly from Old English 'bill', meaning a sword, and is the same root as the bird's beak word, both sharing that ancient Germanic sense of a cutting edge. Soldiers called 'billmen' carried these weapons, and the word survives in 'billhook' today.
What makes 'bill' so wonderfully strange is that it has become a single, ordinary-looking word sheltering three entirely separate histories inside it — the beak of a bird, the blade of a weapon, and the paper that tells you what you owe. Few words in English carry so much hidden variety. Every time someone asks for the bill at a restaurant, they are unknowingly reaching back to a 14th-century Anglo-Norman word for a wax-sealed document, while the duck on the pond beside them uses a completely different 'bill' that has been part of the English language since before the Norman Conquest.