In everyday English, pain names the unpleasant bodily feeling that follows injury, illness, or strain, and it also names grief, embarrassment, or other mental hurt. In the plural it can mean the contractions of childbirth, or the extra trouble someone takes over a task. Informal speech even uses the word for a person or chore that merely irritates. That spread of senses looks like a family of feelings. Historically it is a family of penalties.
The origin of the word pain is easier to see once the modern medical reading is set aside. English did not inherit this noun from Old English the way it inherited sore, which once covered a wider field of hurt. Pain arrived as a loan.
A French borrowing, not a native heirloom
Middle English wrote it peyne, payne, and similar spellings, taking the form from Old French and Anglo-Norman peine (also paine). Those French forms go back to Latin poena, a word for punishment, a penalty, and repayment. In later Latin the same noun could already mean torment and hardship, so the leap from legal cost to felt suffering had begun before English borrowed it.
Dictionaries do not all round the first English dates the same way. Some give the fourteenth century as a convenient label. More detailed records place the noun in the late thirteenth century for the agony of Christ, and around 1300 for criminal punishment, for ordinary bodily hurt, and for the torments imagined after death. The path itself is not in dispute: this is a French word on a Latin stem, not a Germanic coinage.
Penalty before sensation
Latin poena is not home-grown Latin. Rome took it from Greek poinē, a term for retribution, a fine, and specifically the compensation paid for spilled blood, the kind of settlement later languages would call weregild. The Greek noun sits on a Proto-Indo-European formation reconstructed as a word for payment, from a root meaning to pay, atone, or compensate.
That root still shows up where English speakers would not expect a cousin of pain. Slavic cena and Lithuanian kaina mean price or value. Greek tinein means to pay; a related Greek noun, timē, covers price, honor, and esteem. Avestan kaena is revenge; Sanskrit has a verb of revenge in the same family. The oldest picture is not a throb in a nerve. It is a bill that must be settled.
English keeps a large legal clan from the same Latin noun: penal, penalty, punish, and the court formula subpoena, whose first element means under penalty. The verb pine, in the sense of wasting away from longing, is another relative that entered English earlier through a different route. German Pein, Dutch pijn, and the Scandinavian pine words are parallel borrowings into other Germanic languages, not descendants of the English noun.
How the meaning moved
Once the word was in English, punishment and suffering sat side by side. A court could impose pain as a penalty, including a fine, not only bodily harm. Preachers used it for damnation. At the same time it named the opposite of pleasure in the body and in the mind. The legal sense did not vanish; it froze in the idiom on pain of death, and in the variants under or upon pain of, where pain still means the penalty you risk, not the ache you feel.
From the late fourteenth century the noun also covered exertion: the cost of effort. By the 1520s the plural pains was established for careful trouble taken to get something done, the sense still alive in take pains. The verb followed a similar curve. Around 1300 it could mean to strive or strain oneself; later in that century it meant to hurt someone physically or to cause grief. Middle English could still use it for punishment and torture.
Much later slang turned the noun into a nuisance. To give someone a pain, in the sense of annoying them, is recorded from the end of the nineteenth century. Pain in the neck is a 1920s localization; ruder variants appear in print in the 1930s, and some lexicographers suspect the coarsest form is older than the polite ones, though that is guesswork because such talk often went unwritten. The compound painkiller, for a drug or herb that dulls the sensation, belongs to the mid-nineteenth century, when the medical sense had long since become the default.
What the history still shows
The most revealing fossil is not the slang. It is the legal phrase. On pain of death still treats pain as a price: break the rule and you pay. That is closer to Greek blood-money than to a headache. English later built a rich medical vocabulary around the same short word, but the history never started in the clinic. It started in a system of payment, penalty, and revenge, and only afterward became the name of what it feels like to be hurt.
If you want a single takeaway, set pain next to price. Slavic cena and English pain look unrelated, yet they are descendants of the same old idea that a wrong, a debt, or a loss has a cost. English kept the suffering and forgot the invoice, except in that one stubborn courtroom formula.