Easton's Bible Dictionary (1897)
(Heb. pethen), Deut. 32:33; Job 20:14, 16; Isa. 11:8. It was probably the Egyptian cobra (Naja haje), which was very poisonous (Rom. 3:13; Gr. aspis). The Egyptians worshipped it as the uraeus, and it was found in the desert and in the fields. The peace and security of Messiah’s reign is represented by the figure of a child playing on the hole of the asp.
Smith's Bible Dictionary (1863)
(Heb. pethen), translated (adder in) (Psalms 58:4; 91:13) Probably the Egyptian cobra, a small and very poisonous serpent, a dweller in the holes of walls, (Isaiah 11:8) and a snake upon which the serpent-charmers practiced their art.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
ASP. Deut 32:33; Rom 3:13. A small but very poisonous serpent, Egyptian Cobra. (Naja huge. ) probably the Egyptian cobra, which dwells in holes. The venom of this reptile is cruel, because it is so subtle and deadly, and requires an immediate excision of the wounded part. For an infant child to play up to the hole of such a venomous reptile would seem to be most presumptuous, and hence the force of the figure used by the prophet, Isa 11:8, to represent the security and peace of the Messiah's reign. See Adder (2).