What is Ad Inquirendum?

Legal Definition
Practice. A judicial writ, commanding inquiry to be made of any thing relating to a cause depending in court.
-- Bouviers Law Dictionary
Legal Definition
To inquire; a writ of inquiry; a judicial writ, commanding inquiry to be made of any thing relating to a cause penning in court. Cowell.
-- Black's Law Dictionary
Legal Definition
A writ commanding an inquiry or investigation.
-- Ballentine's Law Dictionary