SUBPOENA, in LAW, a writ whereby common persons are called into chancery, in such cases where the common law hath provided an ordinary remedy; and the name of it proceeds from the words therein, which charge the party called to appear at the day and place affirmed, sub pena centum librarum, &c. The subpoena is the leading process in the courts of equity; and by statute, when a bill is filed against any person, process of subpoena shall be taken out to oblige the defendant to appear and answer the bill, &c.