John Calvin on Romans 3:14-15

14. Then he says, that their mouth is full of cursing and bitterness Psalm 10:7. Paul corrects the order of the words as found in the Septuagint, and gives the Hebrew more exactly, but retains the word “bitterness,” by which the Septuagint have rendered מרמות, which means deceit, or rather, mischievous deceit. Some think that it ought to be מררות, “bitterness;” but there is no copy in its favor. — Ed. — a vice of an opposite character to the former; but the meaning is, that they are in every way full of wickedness; for if they speak fair, they deceive and blend poison with their flatteries; but if they draw forth what they have in their hearts, bitterness and cursing stream out.