Three histories behind one spelling
Ask for the origin of the word bill and you are not asking about a single English noun. The restaurant check, the draft law, the banknote, the duck’s beak, and the hooked blade on a pole all share a short modern spelling. They do not share one root. Two of the nouns are native, from Old English. The third is a medieval borrowing that began as a name for a seal and then for the paper under the seal.
That collision is easy to miss because the paper senses now dominate everyday speech. The older native words never disappeared. They simply occupy narrower corners: ornithology, headlands, farm tools, and a few idioms.
From a round seal to official paper
The invoice, the statute, the poster, and the dollar note belong to the borrowed line. Middle English had bille, taken from Anglo-French bille and from the Anglo-Latin form billa. Those spellings are a medieval reshaping of Latin bulla. In classical Latin the word named a rounded lump: a bubble, a boss on metal, a neck amulet. In later chancery practice the round lump was the lead or wax seal on a charter. The name then moved from the seal to the sealed writing, and from there to formal writing in general.
English also has bull for a papal decree. That is the same Latin noun on a different path. Bill and bull are doublets: one came through the billa/bille spelling used in English administration, the other kept a form closer to Church Latin. American Heritage traces the document noun through Norman French and Medieval Latin billa as an alteration of bulla. Dictionary treatments that start from Anglo-French and Anglo-Latin are describing the same arrival.
By the late fourteenth century the borrowed noun could mean a formal document, a plea or charge in court, even a personal letter. Around 1400 it already covered a written account of goods or work and the sum owed. Late in the fifteenth century it could be a public notice put up where people would see it, the source of later playbill and handbill. From the 1510s it named a draft statute laid before a legislature. An order directing one person to pay another is recorded in the 1570s. Paper money as a bill appears in the 1660s. The verb, to send someone a statement of charges, is later still, from the 1860s.
Once the word meant official paper, English kept attaching the same noun to lists, notices, drafts of law, and notes that stood in for coin.
How the paper senses branched
The legislative use still carries the old official flavor. A bill in parliament or congress is not yet an act. It is a text offered for debate and enactment. Historically that sense passed through petition: a request to the sovereign that included the wording of the desired statute. Public bills later lost the petitionary frame. Private bills, which grant relief or privilege to a named person or body, still begin as petitions in some systems.
Commerce froze the inventory sense in set phrases: bill of lading, bill of sale, bill of health, bill of exchange. Bill of fare is a menu under another name. Bill of Rights keeps the older meaning of a formal written statement of particulars, not an invoice. Theatrical English left two common idioms. Fill the bill and fit the bill come from the posted programme: a performer or an item that matches what the notice promised.
In North American speech, bill for paper money is ordinary. That is the seventeenth-century bank-note sense, not a separate coinage. Slang that treats a bill as a hundred dollars, or in Britain a hundred pounds, is a later narrowing of the same paper-money track. Foot the bill stays with the charge-sheet sense: to pay what the account demands.
Beak, headland, and hooked steel
The bird’s bill is native. Old English had bile for a beak, and also for an elephant’s trunk. Sources do not agree on how tightly that noun is bound to the weapon word. Some dictionaries treat the beak as related to a poetic Old English word for a hooked sword, or to an Old High German bil meaning pickaxe, on the likeness of shape. Others mark the origin as unknown and only then offer a possible special use of Old English bil or bill for a hook or sword. A cautious older account already noted that a bird-bill word of this shape is not clearly attested as a shared Germanic inheritance outside English. English has an Old English beak noun; it may be a transferred cutting-tool word; the transfer is not proven.
The weapon is firmer. Old English bil or bill named a sword, especially one with a hooked blade, and a chopping tool. It continues a Proto-Germanic form reconstructed as bilją, a cutting or chopping implement. Close relatives include Dutch bijl and German Beil, both meaning axe, with older matches in Old Saxon bil, Middle Dutch bile, Old High German bihal, and Old Norse bilda for a hatchet. A deeper Indo-European root meaning to cut or strike is often proposed. That deeper step is possible rather than settled. An older encyclopaedia entry even denied a link with German Beil; modern dictionaries include it among the cognates.
The military bill became a long-handled infantry weapon with a hooked or bladed head, still familiar in English armies into the sixteenth century. The shape survives in the billhook and the hedging bill used to cut brush and lay hedges. Place-names such as Portland Bill use the beak sense: a pointed spit of land. American Heritage also records bill for the visor of a cap and for the tip of an anchor fluke, both extensions of a projecting point.
From the beak noun came a verb. Doves stroke bills. By the 1590s the verb could describe lovers who caress. Bill and coo has been a set phrase since the later eighteenth century.
What the spelling conceals
Keep the doublet if you want one fact that splits the histories. A papal bull and a restaurant bill share Latin bulla, the round seal that named the document. A duck’s bill and a billhook sit on the native side, either as one Old English cutting shape or as two neighbours that English never fully proved to be the same word. The identical modern spelling is a collision, not evidence that money, law, and birds grew from a single root.