Ang(a) /Ong(a). - possible Old English term for the Angon.
It seems that the javelin has a number of designs and that the angon alone is a variant of the pilum. Agathias gives an excellent description of the angon used by the Franks in the 6th century:
Angon - heavy Germanic javelin, typically with armour-piercing bodkin head and barbs.
Bebra - name given by Vegetius for Barbarian pilum.
Franca - O.E. word glossed “lance, javelin” - the typically long-necked ‘Frankish’ Angon.
Gaesum - barb-headed heavy javelin used by Roman Auxiliaries of Celtic origin. Essentially, a barbed pilum.
Lancea - light dual-purpose spear. Typical weapon of Late Roman Infantry.
Pïl - O.E. word, glossed “..arrow, dart, javelin.”
Pilum - Roman heavy javelin, with long iron head.
Spiculum - heavy (?) javelin used by Late Roman Infantry but with a much shorter head than the earlier pilum.
Verutum - light javelin used by late Roman Infantry.
“The Angons are spears which are neither very short nor very long; they can be used, if necessary, for throwing like a javelin, and also in hand to hand combat. The greater part of the angon is covered with iron and very little wood is exposed. In battle the Frank throws the angon, and if it hits an enemy, the spear is caught in the man and neither the wounded man nor anyone else can draw it out. The barbs hold inside the flesh, causing great pain, and in this way a man whose wound may not be in a vital spot dies. If the angon strikes a shield, it is fixed there, hanging down with the butt on the ground. The angon cannot be pulled out because the barbs have penetrated the shield, nor can it be cut off with a sword because the shaft is covered with iron. When the Frank sees the situation, he quickly puts his foot on the butt of the spear, pulling down, and the man holding it falls leaving his head and chest unprotected. The unprotected warrior is then killed either by a stroke of the axe or a thrust with another spear.”
I am not sure if the angon as such is that distinctive from the overall class of weapons that we might designate 'heavy javelins': that is, javelins desinged to impede enemy shields/armour through the use of barbed heads and long metal shanks. Certainly these 'heavy javelins' can be seen as far back as the Celtic gaesum. It is said that the weapon heads were technically work-intensive and therefore angon/pilum type weapons in a Germanic context were high-prestige weapons reserved for use against similar high-status warriors who's armour required armour-piercing ranged weapons as a result.