A formal written document. (Merriam – Webster)
Specifically: a legal instrument in epistolary form issued under seal in the name of the English monarch (Merriam – Webster)
An order or mandatory process in writing issued in the name of the sovereign or of a court or judicial officer commanding the person to whom it is directed to perform or refrain from performing an act specified therein. (Merriam – Webster)
A form of written command in the name of a court or other legal authority to act, or abstain from acting, in a particular way. (Oxford Dictionaries)
A Crown document summoning a peer to Parliament or ordering the election of a member or members of Parliament.(Oxford Dictionaries)
A former order seal, issued in the name of a sovereign, government, court, or other competent authority, enjoining the officer or other person to whom it is issued or addressed to a do or refrain specified act. (Dictionary.com)
A legal document from a law court that tells you that you will be involved in a legal process and explains what you must do. (Cambridge Dictionary)
My creditor sent me a writ of summons. What am I supposed to do?
Writs and pleadings. Citizens information.