Well, there’s a bow in the character, so that seems like a possibility. 単 alone expresses the idea of singleness, though I don’t know if that’s relevant.
Anyway, Kanjipedia says that it represents pulling back on a device meant for launching pebbles and causing the string to vibrate. The Chinese etymology site I like to use says that it originally represented a slingshot with a shot on the string, and referred to the slingshot or to the pellets it was used to shoot. I guess that’s linked to most of the use cases you mentioned?
That was exactly my assumption — nice to see it confirmed!
I just looked up kanjipedia. Thanks for the reference.
What’s the Chinese etymology site you use? (I don’t speak a word so doubt I’ll be able to use it without help from my Chinese friends, but it might be worth a bookmark).
This one: http://qiyuan.chaziwang.com
I don’t know what exactly their sources are, but I like all the drawings and how those are often linked to meanings.