浴神不死 是謂玄牝
[yu4] [shen2] [bu4] [si3] [shi4] [wei4] [xuan2] [pin4]
The spring spirit doesn’t die, it is called the dark [black, mysterious] female
谷神不死，是謂玄牝。
[gu3] [shen2] [bu4] [si3] ， [shi4] [wei4] [xuan2] [pin4] 。
The valley spirit doesn’t die, it is called the dark [black, mysterious] female
A fertile valley produces an abundance of crops and is a safe haven overall for those living in it; a spring produces what can be considered infinite water. As life springs from the female, so does life spring from these forces. This force is female and brings forth life. This mysterious female force is the Yin in the traditional Yin and Yang.
This could be either “spring” or “valley”. If we look at the 康熙字典 we get: 浴：《唐韻》余蜀切《集韻》《韻會》兪玉切，𠀤音欲。《說文》洒身也。《周禮·天官》宮人共王之沐浴。《註》浴用湯。又借爲潔治意。《禮·儒行》儒有澡身而浴德。又《夏小正》十月黑鳥浴。黑鳥，烏也。浴謂乍上乍下也。又水名。《山海經》泰冒之山，浴水出焉。又隂山，濁浴水出焉。又幽都之山，浴水出焉。又《韻補》叶欲屑切，音悅。《蘇軾·月硯銘》其受水者哉生明，而運墨者旁死魄。忽𤣥雲之霮䨴，觀玉兔之沐浴。《集韻》或作𣴲。
Once you see the older definition from the 山海经, you see that it is a definition for a spring. This could be a character which was changed out for rhyming reasons or similar, or potentially a change in meaning for characters. My evidence for it being for “valley” is more in line with the original character’s representation and the fact most other editions use 谷. Ultimately, I wouldn’t read too much into it either way since it really doesn’t affect either reading of this section or the next few.
玄牝之門 是謂天地之根
[xuan2] [pin4] [zhi1] [men2] [shi4] [wei4] [tian1] [di4] [zhi1] [gen1]
The dark [mysterious, black] female’s gate, is called the origin of Heaven and Earth
玄牝之門，是謂天地根。
[xuan2] [pin4] [zhi1] [men2] ， [shi4] [wei4] [tian1] [di4] [gen1] 。
The dark [mysterious, black] female’s gate, is called the origin of Heaven and Earth
I took a Chinese history course that covered some degree of literature, and one common euphemism for a woman’s genitals was either a “gate” or a “jade gate”. Here, we are effectively saying the the female force birthed “Heaven and Earth” (or all of existence). As touched on before, the “dark” is the Yin in Yin and Yang, coupled with the female force (which is also traditionally Yin). Both sides of existence are required in order to conceive. Male and female are required to create a life, but we are ultimately saying that existence is actually born from the feminine force of the universe.
綿綿呵若存 用之不堇
[mian2] [mian2] [a1] [ruo4] [cun2] [yong4] [zhi1] [bu4] [jin3]
It is wispy and ethereal [lit. cotton], as if it only exists, [though] when used it does not dwindle [lessen]
綿綿若存，用之不勤。
[mian2] [mian2] [ruo4] [cun2] ， [yong4] [zhi1] [bu4] [qin2] 。
It is wispy and ethereal [lit. cotton] as if it only exists, [though] when used it does not weaken [康熙字典: sicken]
This feminine force is ethereal and wispy. The phrasing is literally cotton, as cotton is light and delicate when in its raw form, but when processed it becomes strong enough to create cloth and rope. Raw cotton is effectively useless until processed as if it is just something there, but this feminine force is deceptive. You can draw from it, but it does not dwindle or weaken when drawn upon like the spring. It is infinite for all intents and purposes and strong when necessary. It is strong enough and infinite enough to give birth to the universe and all things in it.