The word seax has multiple meanings and spellings.
The seax is a "traditional" (i.e. well-out-moded) English weapon. It is a sword, with a slightly-curved blade which flares out from the pommel to a broad end, which is then cut off at an angle. In general the outer curve and the sharp end are the bladed edges, with the top, straight, margin, left blunted. There is also a small half-circle taken out of this upper edge toward the "point", possibly as a blade-catcher.
A seax, sax, saex or saxon knife is also an Anglo-Saxon or Scandanavian eating and working knife, sturdily made with a straight cutting edge and a curved back which tapers to the point. Shorter versions might be refered to as a scramasax and a longer version which appears to have served as sword substitute and was known as a langsax. Known throughout Western Europe from after the decline of the Roman Empire, but only appears around 600 CE in Saxon England.
They were frequently pattern welded.