Sub poena is Latin for Under a penalty
sub poena, sub pena Under punishment or penalty. A sub poena is a court order requiring a person to appear in court, usually unwillingly, on pain of punishment if he/she does not do so. Usually a sub poena is ordered so someone can give evidence or 'bear witness' for a specified legal trial.
a writ requiring a person to appear in court - originally fully under penalty of a fine/imprisonment/etc., so that the potential punishment would appear after the words sub poena, which is nowadays usually rendered as a single word, subpoena
(Latin) literally under penalty; in English, this phrase has become a single word â€` subpoena â€` and is a document that requires the recipient to appear in court.