Truncheon, as you might expect, is a word with some French history. It first appeared in our language, as far as we know, around the 14th century, when it went under the Middle English umbrella as tronchoun. Its parentage was the Anglo-French word, trunchun, and that in turn goes way back to the Vulgar Latin word truncion/truncio, which comes from the 'proper' Latin word, truncus, which means a trunk. I suppose there's a connection between a trunk (the trunk of an elephant?) and the baton we know today, but it seems a bit of a distance.
Stanchion (to go back to where we started in this post) initially has a similar history: Middle English stanchon, Anglo-French stanchun or stançun. These words, however, were alterations of an Old French word, estançon, which is apparently a diminutive of estance, meaning a stay or a prop. At least stanchion starts where it ends, you might say. [Thanks, Merrian-Webster, by the way.] Estance is a fancier ancestor to have than truncio, I think, even if it's not quite a old.
It just occurs to me that in our usual English spelling fashion we have managed to make one of these words end in 'ion' and the other in 'eon'. Ain't English fun?
Perhaps because stanchion has retained its original meaning rather more, it tends mostly to relate to things that stand upright and hold something else. Those little things you see in restaurants where they hold the number of your order are a form of stanchion, I suspect, though I don't know if they're actually called that. Stanchions appear in restaurants more as a form of crowd control: they'll often have a rope dangling between them to stop unworthy patrons from joining worthy ones. [See the fancy model to the right.] I notice them mostly in banks where they force people to form queues, and where children delight in dropping the connecting 'rope' (of whatever form) off one stanchion, find they've just received a disapproving look from a parent, and then have to figure out how to put it back again.