Boyd’s Bible Dictionary:

(crocodile like.) The basilisk (Jer. 8:17; Isa. 11:8; 14:29; 59:5); in all which some species of hissing, venomous serpent is meant.

Concise Bible Dictionary:

What reptile is alluded to is not definitely known: the Hebrew words tsepha (Isa. 14:29 only) and tsiphoni are from “to hiss.” The texts in which they occur refer to its dangerous character. Its deadly sting will be changed in the millennium, when a little child shall put its hand on its den. Of Israel it is said figuratively “they hatch cockatrice’ eggs” (Isa. 11:8; 59:5; Jer. 8:17). The latter word is translated “adder” in Proverbs 23:32.