tressure
A narrow border near the edge of a shield or banner.
The official blazon of the arms of Perth is "Gules, a Holy Lambe passant regardant staff and cross argent, with the banner of St. Andrew proper, all within a double tressure counter-flowered of the second": […].
Where it comes from
From Middle English tressour, from a mixture of Old French tressure and tresseor. By surface analysis, tress + -ure.
Adapted from the Wiktionary entry tressure (CC BY-SA 4.0).