According to many commentators (Ibn Ezra, Chizkuni, Sforno) לא תנאף does not only mean "Do not commit adultery". It ALSO includes any type of prohibited sexual acts.
According to the Talmud (Niddah 13b) the verse also includes proscribes male masturbation.
תנא דבי רבי ישמעאל "לא תנאף", לא תהא בך ניאוף בין ביד בין ברגל
ביד - מוציא זרע לבטלה
The "big ten" are basically category headers for the major categories of Mitzvos (see Rashi on Shemos 24:12). Stealing is the archetypal example of property crimes, and "Do Not Steal" is the main prohibition is the larger category of property crimes and respecting others property, generally. Adultery is the archetypal sexual sin, and it serves as the header ...