This verse ought to be translated, He that hideth hatred is [a man] of lying lips, and he that uttereth slander is a fool. He who cherishes hatred in the heart must be a liar and a hypocrite, speaking and acting in a way contrary to his real sentiments; if he divulges his slander, he is a stupid fool, injuring his neighbour, and procuring ill will for himself.
The LXX. reads, "Just ( δίκαια) lips conceal hatred;" but probably δίκαια is an error for ἄδικα or δόλια, though Ewald defends it, and would alter the Hebrew to suit it.