poena

Poena, poenae is feminine, first declension, borrowed early from Greek poine, a blood-price paid to a dead man's family. The commercial origin survives in the standard idiom: "poenas dare" is to pay the penalty, so the guilty man is the subject, while "poenas sumere" or "poenas repetere" is to exact it. Getting those backwards reverses who is being punished, which is not a small mistake.

Church Latin adds the pains of hell and of purgatory, so poena there is suffering as much as sentence. English gets an unusually large crop from it: penal, penalty, punish, penitent, impunity, subpoena (under penalty) and, through French, pain itself.