A string connecting a pair of mittens or gloves to prevent their loss, worn around the shoulders or (especially by children) threaded through the sleeves of a coat, etc.
Origin
Late 19th century.
Definition of mitten string in US English:
mitten string
noun
A string connecting a pair of mittens or gloves to prevent their loss, worn around the shoulders or (especially by children) threaded through the sleeves of a coat, etc.