"He who conceals hatred has lying lips, and he who spreads slander is a fool"
conceals
This is the Hebrew word kasa, which means to cover, conceal, hide.
hatred
This is the Hebrew word saneh, which is a strong emotional word which means oppose, detest, despise.
Solomon is trying to say that someone who has this kind of emotional response to a person will lie about them if they try and conceal that they have such a negative emotional reaction to them.
slander
This is the Hebrew word dibba, which means defaming, evil report. The idea is either emphasizing the negative or using the negative to ruin another person's reputation.
Solomon declares that a person who would ruin another person's reputation through slander is a person who is extremely selfish. Look out for that selfishness. It will turn on you.
Until tomorrow,
Gil Stieglitz