thirdboroughthridborrown.

Etymology: In 15th cent. thridborro , 16th cent. thridborowe , later third-borow ; and with both elements variously corrupted. Early evidence of origin scanty; but, as pointed out by Professor Skeat, probably a Middle English corruption of fridborgh < Old English friðborg peace-pledge, peace-surety: see frithborh n., frank-pledge n. The corruption may have been due to Norman scribes, but not necessarily so: see etymological note and compare th n.¹ (6). Compare borrowhead n.², borsholder n., headborough n.The friðborh or frithborgh was originally the ‘association of ten men in common responsibility’ to prevent crime and breach of the peace. In Middle English legal use the word was worn down to fridborgh , friborg , and freoborg , and, the first element being associated with freo ‘free’, was rendered in Anglo-Norman frank plege , Anglo-Latin francum plegium . The head man of the frithborh was in the 12th cent. called friðborgheved or frithborges heved , ‘head of the frithborh’ ( Laws of Edw. Conf. 20 (or 19), §3), and was later known as bor(r)owhead , head-bor(ou)gh , bor(h)s-holder , and burrow-elder ( < *borh-ealdor ), also in Anglo-Latin plegius capitalis ‘head or chief pledge’. In Fleta i. xlvii. §10, it is said, ‘frithborgh [printed frich-] est laudabilis homo astrarius testimonii…per quem omnes iuxta ipsum commorantes firmiori pace sustententur sub stabilitate fideiussionis eius vel alterius per denarium numerum, unde quilibet est quasi plegius alterius’. In this we see the transition of frithborh from the association to its individual members, and esp. to the headborough. In certain cases the latter acted with two of his fellows, ‘duos de melioribus suorum frithborgorum’ ( Laws of Edw. 20 (or 19), §3), and this association of three may have contributed to the change of name fromfridborgh to thridborgh and thirdborough . The probable connection of thridborow with freoborh was suggested by Cowell: see quot. 1607.Previous versions of the OED give the stress as: ˈthirdborough.