A more thorough explanation:

Definition: A tubman was a junior barrister in the Court of Exchequer who made motions that were second in precedence to those of the postman. The name "tubman" comes from the fact that they stood by a tub that was used as a measure of capacity.

Example: In the Court of Exchequer, the postman had the highest precedence when making motions, followed by the tubman. The tubman would make motions after the postman had finished.

Explanation: The example illustrates how the tubman was a junior barrister who had a lower rank than the postman in the Court of Exchequer. The tubman's role was to make motions that were second in importance to those of the postman. The name "tubman" comes from the fact that they stood by a tub that was used as a measure of capacity. This historical term is not commonly used today.