Definition of "seax"

The Pugio or Dagger was used by the Romans, a species of that weapon called the Hand Seax was worn by the Saxons, with which they massacred the English on Salisbury Plain in 476.

1786, Francis Grose, A Treatise on Ancient Armour and Weapons, page 34

It consisted of the arms of the City of London, Middlesex (three seaxes, or Saxon swords), Buckingham (a swan), and Hertford (a hart), arranged quarterly, on a background of crimson and ermine mantling […] .

1950 June, Michael Robbins, “Heraldry of London Underground Railways”, in Railway Magazine, page 380