What is the "sensual desire" fetter?

- What is the "sensual desire" described as one of the fetters, which is: - Reduced or weakened in a once-returner - Abandoned in a non-returner - Are *kāmarāga* and *kāmacchando* used interchangeably? - Does it have a specific meaning, perhaps identified in a sutta or commentary -- or can we only imagine what it means by analysing the words (kāma, rāga, chanda)? For example, the words *micchacara* and *abrahmacariya* -- used in the two versions of the 3rd precept -- have explicit canonical definitions (or at least specific examples of prohibited behaviour) beyond what can be inferred from only the etymology of the words. - What about any "exceptions which prove the rule" in suttas which describe arahants -- for example the Buddha's experiencing discomfort of old age in [DN 16](https://suttacentral.net/dn16/en/sujato) : > Sometimes the Realized One, not focusing on any signs, and with the cessation of certain feelings, enters and remains in the signless immersion of the heart. Only then does the Realized One’s body become more comfortable. Are we to understand there's no "desire" associated with this? That it's not "sensual"? Or perhaps that it is if anything a desire for "neutral" feelings (i.e. for *not* feeling pain), and therefore within the scope of enlightened thinking? - If the senses are the All ([SN 35.23](https://suttacentral.net/sn35.23/en/sujato)) , are there any desires which aren't "sensual" -- even a preference for seclusion, for example, or for good health? Or even, for morality?