One of the mysteries of the English language finally explained.
Definition of blue-stockinged in English:
blue-stockinged
adjective
archaic1Wearing blue stockings. Also (and in earliest use) figurative: belonging to or characteristic of a person (such as a countryman, tradesman, puritan, etc.) who wears plain blue worsted, as opposed to black silk, stockings (now rare).
2Chiefly derogatory. Especially of a woman: that is a bluestocking; learned, scholarly, literary, intellectual.
Origin
Mid 17th century; earliest use found in John Cleveland (bap. 1613, d. 1658), poet. From blue + stockinged.