Basilsk is a large serpent or snake. The general idea of a huge snake would also apply because anything very large and long could be referred to as a basilsk.

Bible occurrences: Isa 11:8; 14:29; 59:5; Jer 8.17.

“King serpent” which is a snake 3 meters long with a head like a crown.

* Basilisk occurs in the D.V. as an equivalent for several Hebrew names of snakes:

* (1) Péthén (Ps. 110:13), the cobra; had the Latin and English translators been more consistent they would have rendered this Hebrew word here, as in the other places, by asp;

(2) Céphá’ and Cíphe ‘ônî (Prov. 23:32; Is. 11:8; 14:29; Jer. 8:17;

(3) ‘éphe’éh (Isaiah 59:5), a kind of viper impossible to determine, or perhaps the echis arenicola;

(4) flying sãrãph (Isaiah 14:29; 30:6), a winged serpent (?), possibly also a reptile like the draco fimbriatus, which, having long ribs covered with a fringe-like skin, is able to glide through the air for short distances.

Source: [http://en.wikipedia.org/wiki/List_of_the_animals_in_the_Bible]