A longchain is a linked chain that was generally more than a meter long. Women wore these tucked into their girdle or festooned across the bodice of a dress. Men sometimes attached a watch to them and put the chain around their neck and the watch in a vest pocket.
Longchains are sometimes referred to as a muff chains and vice versa. A muff chain was long enough, when worn around the neck, to pass through a lady's hand warmer and the ends could be attached to each other thus suspending the muff. These were popular in the 18th century.