CathInfo.com

And cussing is a sin, as St. Alphonsus and St. Paul teach:

”But, ” says St. Paul, “fornication and all uncleanness, let it not so much as be named among you, as becometh saints.” (Ephes. v. 3.) Mark the words”all uncleanness. ” We must not only abstain from obscene language and from every word of double meaning spoken in jest, but also from every improper word unbecoming a saint that is, a Christian ... Reflect, says St. Augustine that your mouths are the mouths of Christians, which Jesus Christ has so often entered in the Holy Communion. Hence, you ought to have a horror of uttering all unchaste words, which are a diabolical poison. ”See, brethren, if it be just that, from the mouths of Christians, which the body of Christ enters, an immodest song, like diabolical poison, should proceed.” (Serm. xv. de Temp.) St. Paul says, that the language of a Christian should be always seasoned with salt. ”Let your speech be always in grace, seasoned with salt.”(Col. IV. 6.) Our conversation should be seasoned with words calculated to excite others not to offend, but to love God. ”Happy the tongue,” says St. Bernard,”that knows only how to speak of holy things!” Happy the tongue that knows only how to speak of God!" https://oneintheirhearts.wordpress.com/2015/08/09/the-vice-of-speaking-immodestly-st-alphonsus-liguori/

Saint Paul says "fornication and all uncleanness". Saint Alphonsus also is quite clear.