Time to tear open the envelope and reveal the answer: tare. Tare names "the weight of a container (or vehicle) deducted from the gross weight in order to obtain the net weight." The tares we started out with—the synonymous clear tare and net tare, the contrasting actual tare and average tare, and the estimated percentage tare—all reflect the importance of distinguishing between container and contents. As you might imagine, such a distinction is important to both merchants and shippers.

Born in the Arabic tarha (meaning "that which is removed"), tare traveled first into Old Italian and then into Middle French before making its way into English in the late 15th century. The royal records of King Henry VII indicate shipments of two barrels of gunpowder weighing, besides the tare, some five hundred pounds.

It's easy to see why seafaring types selected tare to represent T in the phonetic alphabet back in the early 1900s, but do you know which word was chosen to replace it? Back in 1957, tare was replaced by tango.