betweenity (n.)

中古英语 bitwene，源自古英语 betweonum，麦西亚方言 betwinum，"在分隔的空间中，中途，在其中； 轮流地"，由 bi- "通过"（参见 by）+ tweonum "两个每个" 的复数形式 *tweon（比较哥特语 tweih-nai "两个每个"； 源自 PIE 词根 *dwo- "两个"）。

Between is literally applicable only to two objects; but it may be and commonly is used of more than two where they are spoken of distributively, or so that they can be thought of as divided into two parts or categories, or with reference to the action or being of each individually as compared with that of any other or all the others. When more than two objects are spoken of collectively or in divisibly, among is the proper word. [Century Dictionary]

Between 只能字面上适用于两个对象； 但通常情况下，它可以用于超过两个对象，前提是它们被分别讨论，或者可以将它们想象为分为两部分或两个类别，或者与每个对象的行为或存在相比较，而不是与其他对象或所有其他对象相比较。当涉及到集体或不可分割地讨论超过两个对象时， among 是正确的词语。[世纪词典]

In all senses, between has been from its earliest appearance, extended to more than two. [OED]

在所有意义上， between 从最早出现时就被扩展到超过两个对象。[OED]

Between a rock and a hard place "陷入困境，处于困难境地" 源自20世纪40年代，最初是牛仔俚语（早期是 between the beetle (hammer) and the block，19世纪末）。Between-whiles "间隔地" 源自17世纪70年代。

这个词缀用于从形容词中构成抽象名词，表示“成为______的状态或品质”，源自中古英语的 -ite，来自古法语的 -ete（现代法语为 -ité），直接源自拉丁语的 -itatem（主格为 -itas），表示状态或品质的后缀，由 -i-（来自词干或连接词）和常见的抽象后缀 -tas 组成（参见 -ty（2））。

Roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. [Fowler]

大致上，以 -ity 结尾的词通常表示形容词所描述的品质，或具体的品质实例，或所有实例的集合； 以 -ism 结尾的词表示倾向或所有感受到这种倾向的人的集合。[福勒]