A.T. Robertson Commentary James 3:8

"But the tongue can no man tame; [it is] a restless evil, [it is] full of deadly poison." — James 3:8 (ASV)

No one (ουδεις). Especially his own tongue and by himself, but one has the help of the Holy Spirit.

A restless evil (ακαταστατον κακον). Correct reading, not ακατασχετον, for which see 1:8. The tongue is evil when set on fire by hell, not evil necessarily.

Full of deadly poison (μεστη ιου θανατηφορου). Feminine adjective agreeing with γλωσσα, not with κακον (neuter). Ιου (poison here, as in Ro 3:13, but rust in 5:3, only N.T. examples), old word. Genitive case after μεστη (full of). Θανατηφορου, old compound adjective (from θανατος, death, φερω, to bear or bring), death-bringing. Here only in N.T. Like the restless death-bringing tongue of the asp before it strikes.