What is Bill To Take Testimony De Bene Esse?

Legal Definition
One which is brought to take the testimony of witnesses to a fact material to the prosecution of a suit at law which is acfually commenced, where there is good cause to fear that the testimony may otherwise be lost before the time of trial. 2 Story, Eq. Jur. § 1813, n.
-- Black's Law Dictionary
Legal Definition
A bill in equity to secure the testimony in a pending action of a witness whose testimony cannot be taken in court. See 4 Del. Ch. 269.
-- Ballentine's Law Dictionary