Probably from an unused root meaning to coil; an asp (from lurking coiled up) -- adder.
H5919. akshub
עַכְשׁוּב noun masculine usually asp, viper (so ᵑ9 ᵐ5; perhaps conject. from sense and "" נָחָשׁ), but perhaps = (? corrupt for) עַכָּבִישׁ spider (q. v.; compare ᵑ7on the passage); — ע ׳חֲמַת Psalm 140:4 a viper's (? spider's) venom is under their lips (see especially Che and references).
עַל see עֹל עלה see III. עלל.