Outer garment made of coarse material worn coat-like by peasantsand ordinary town dwellers; later, c. 1420–50, worn as an open garment by aknight over his armour and displaying his armorial bearings.
*Source: A Dictionary of Medieval Terms & Phrases by Christopher Coredon with Ann Williams
From the prologue of Chaucer’s Canterbury Tales:
In a tabard he rood, upon a mere.
Ther was also a Reve and a Millere,
A Somnour and a Pardoner also,
A Maunciple, and myself, ther were namo.
The Millere was a stout carl for the nones,