Adam Clarke on James 3:8

But the tongue wan no man tame - No cunning, persuasion, or influence has ever been able to silence it. Nothing but the grace of God, excision, or death, can bring it under subjection.

It is an unruly evil - Ακατασχετον κακον· An evil that cannot be restrained; it cannot be brought under any kind of government; it breaks all bounds.

Full of deadly poison - He refers here to the tongues of serpents, supposed to be the means of conveying their poison into wounds made by their teeth. Throughout the whole of this poetic and highly declamatory description, St. James must have the tongue of the slanderer, calumniator, backbiter, whisperer, and tale-bearer, particularly in view. Vipers, basilisks; and rattlesnakes are not more dangerous to life, than these are to the peace and reputation of men.