Porneia is a term the WTS uses for a larger group sexual behaviors that are considered df'able. Fornication is one of those behaviors in the larger group called "porneia."
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w042/15p.13par.15MaintainChastitybySafeguardingYourHeart***The Greek word por·nei´a, translated "fornication," has a fairly broad meaning. It relates to sexual relations involving persons not married to each other and focuses on the misuse of the sexual organs. Por·nei´a includes such acts as oral sex, anal sex, and masturbating another person—conduct commonly associated with houses of prostitution.
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w0011/1p.8par.6AGodlyViewofMoralCleanness***What is meant by the word "fornication"? It comes from the Greek word por·nei´a, which is sometimes used to apply to sexual relations between unmarried people. (1 Corinthians 6:9) Elsewhere, such as at Matthew 5:32 and Matthew 19:9, the term is broader in meaning and refers additionally to adultery, incest, and bestiality. Other sexual practices between individuals not married to each other, such as oral and anal sex and the sexual manipulation of another person’s genitalia, can also be designated as por·nei´a. All such practices are condemned—either explicitly or by implication—in God’s Word.—Leviticus 20:10, 13, 15, 16; Romans 1:24, 26, 27, 32.