A quick look at the meaning of "zwischen" and some related words, particularly "zwischendurch" and "inzwischen" and how that's different to "während".
zwischen, dazwischen, inzwischen, zwischendurch, der Zwischenstop, während, derweil
The core idea of this root was:
And there are basically four big branches we can identify. The first one is duo, and here the sense of two is pretty obvious.
- doubt (“on two sides)”
- dubious (“two faced”)
- duplicity (“two faced”)
The next branch is around the syllables: di-, dia-. In some words in this branch the idea of two is pretty clear. Others are about a theme of through which is probably an extension of the idea of from one side to the other.
- carbon dioxide (“carbon with two oxygen”)
- diploma (originally “official paper folded twice”)
- diabetes (“passing through”, referred to excessive peeing)
- diarrhea (“flowing through”, referred to.. well… you know)
- diagram (“marked/bordered by lines”)
The third branch is bi-.
Here, the theme of two is also very strong, but sometimes it’s fairly obscured.
- binocular (“two eyes”)
- biscuit (“cooked twice”)
- combine (“make two, put together”)
- balance (originally “scale with two pans”)
Last but not least, we have the Germanic branch of two, twi- and zw(e)i.
Besides the actual numbers, this branch has a quite a few words that are about coming from two sides.
- two, zwei, twelve, zwölf, twenty, zwanzig
- twilight (“double light”)
- between (“by/within two”)
- twine, twist (probably originally about “twisting two threads together for a rope”)
- twig, Zweig (branch splitting up “two ways”)
- Zweifel (“on two sides”)
- zwicken (to pinch – “pinch between two”)
- zwingen, Zwang (to force – “pinch between two”)
The connection of “Zweck” was an assumption in etymological sources for a while, but it’s not supported by newer research. Still, I decided to include it here.