The literal translation is most often “rope end,” but when written is more strictly translated as the “rope butt/buttocks/ass” due to the use of the kanji 尻. Therefore, a little more loosely and to capture the play on words, it can translated as the “ass-end of the rope” in English. This word play is almost certainly intended as there are at least three other kanji better suited to to be interpreted as “end” and another kanji set commonly used for “rope end.”
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https://www.nihongomaster.com/japanese/dictionary/word/85117/nawajiri-縄尻-なわじり
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The term Nawajiri used for anything other than simply the ends of the rope seems to be first used and specific to Yukimura Haruki and his school or ryu. This is the reason for definition 3. The most elaborate explanation readily available online is found at https://fetlife.com/groups/115140/posts/6677929 as written by Ugo and is hereafter quoted in its entirety.
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縄尻(Nawajiri, Nawa-jiri): "Nawajiri" is the cardinal concept of Yukimura-ryu. And, its usage is quite unique to Yukimura-ryu.
Generally, "Nawajiri" means "the end of rope", especially "the open end of rope" when it is folded double up (the another end is called "縄頭”（Nawa-gashira）or "縄先" (Nawa-saki). Therefore, "Nawajiri" indicates just a portion of rope in general.
However, Yukimura expands the meaning of "Nawajiri" beyond it. He uses "Nawajiri" so that it would mean "the rope that controls the emotions of bottom". "Nawajiri" does not mean the position of rope. Yukimura uses the word based on "functional classification" of ropes (it is interesting to note that, in Hojojutsu, "Nawajiri" seems to mean the rope for conducting criminal. So, it is "functional classification").
In Yukimura-ryu, "Tome" or "Musubi" is first formed at "near the wrist in Gote-shibari", "ankle", "Neck" or "Hair". He called this procedure as "Nawajiri o toru". And then, hold the another end of the rope (it is "Nawajiri" in general meaning), and start to control the emotion of bottom by changing the "strength", "directions" and "quality (I want to discuss later)" of drawing the rope. At the same time, we receive the feedback signals from the bottom through the "Nawajiri" rope. So, in Yukimura-ryu, "Nawajiri" is the rope that has the function to connect the emotions of top and bottom.
縄尻を取る(Nawajiri o toru): The action to form "Tome" or "Musubi" at either of "near the wrist in Gote-shibari", "Ankle", "Neck" or "Hair". In the lessons, he gives instructions like "Tekubi ni Nawajiri o totte kudasai", meaning "Let's make the starting point of "Nawajiri" rope near the wrist". Sometimes, especially in the case of "hair", we don't have to use rope to take "Nawajiri", instead, draw her hair just by our hand. In this situation, he also expresses like "Let's take Nawajiri of her hair by your hand".
縄尻を引く(Nawajiri o hiku): Start to control the emotion of bottom by changing the "strength", "directions" and "quality" of drawing "Nawajiri" rope. In the lessons, he gives instructions like "Nawajiri o hi-ite", meaning "Let's communicate with the bottom through "Nawajiri".
縄尻で遊ぶ(Nawajiri de asobu): Enjoy the communication with bottom by controlling Nawajiri rope.
Please note the usage of "Nawajiri" in Yukimura-ryu is unique to his school. If you use "Nawajiri" for the Japanese who doesn't study Yukimura-ryu, it means no more than the end of rope.
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