AS gold or silver coin minted from c.630, at first copying Roman style, then after c.660 adopting distinctive AS decoration. Though initially issued in gold, by c.650 the thrymsa was being alloyed with silver; by 675 it was a wholly silver coin. In c. 1000 the thrymsa was equal in value to 3d. [< Lat. tremis = a Roman coin]
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.