Hisbonenus is essentially the idea of looking intensely into the depths of a topic and going over it a lot until one understands it clearly with all its parts in particular detail. And this is the innerness of Binah (understanding) which is called in the language of the Talmud Iyun.
For there are three things in every intellectual concept: the depth, length and width. The width is the aspect of the explanations of the concept to every side (from every angle).
And the length is the immense lowering of the intellect to enclothe the concept in various allegories until it is brought down to the grasp of a little child etc.
And the depth of the concept is the aspect of its quintessential (self) point the way it is. And this is called the depth of the Musag (the idea as it is in Binah) since everything that spreads out in the explanations of the idea to every side with a great width with several details and also too the length with the immense bringing down (of the intellect) as well as to the heights above, (i.e.) to understand from it (from the depth of the Musag) even more into levels that are much higher than it (the original idea) all this comes out of the essence of the depth of its point the way it flows out from Chochmah which is called Ein (non) (meaning non-existing - the non apprehended point of wisdom) and as it says "a river flows out of Eden" for Binah (understanding) is called a river and Chochmah is called a spring as is known.
And Now Chapter 1.07
And this is what is called Eeyun, namely that one thinks over an idea and scrutinizes it meticulously. This being a slow methodical study, the opposite of rushing through a subject. The purpose of this being in order to come to the depth of the idea specifically the way it is in the essence of its internal and true inner most point, as it is connected to its source in the wellspring of Chochmah. As a person examining an object with his eyes and not just merely with a passing glance, but rather, with great discernment and an attentive eye, examining it with great precision. Until he is quite familiar with the object, with all of its parts and inner workings. Like, an archeologist who through careful examination can discover many things from a shard of a ceramic pot, all totally unapparent to the untrained eye. Or an electrician carefully disassembling a device, examining all of its inner workings. So that when he’s done he can tell you more than just what it does. Similarly, an antique dealer, when he sees something he knows how to examine its inside and out to determine its true value. This type of careful analysis is what is called Hisbonenus and it is for this reason that it is spelled with a double letter ‘Nun,’ (; hisboNeNus rightfully according to Hebrew grammar the word should really be spelled with one Nun, making it Hisbonus, and not Hisbonenus, the doubling of a letter in Hebrew grammar represents a specific stress) here this stress is hinting at the fact that one must examine it a lot, reviewing it over and over. As Rashi (Rabbi Shlomo Itzchacki, the most fundamental Jewish commentator on the TaNa"Ch and Talmud, the title Rashi being an abbreviation of his name) defines Eeyun -"to stand over something until it is understood clearly" and not moving on to the next subject until the first is understood.