Found: an etymology for kʰíyəp ‘dark’
kʰíyəp ‘darkness, dark’ is said in the 2012 Grand Ronde dictionary to be “of obscure origin”.
So to speak.
Dark in Clackamas (image credit: Puzzle Box Horror)
That characterization sent me looking into less-usual source languages, but e.g. K’alapuyan has an only vaguely similar root for ‘dark’, e.g. in gi-di-húʔyuʔ ‘(when) it got dark’.
And Southwest Washington Salish languages are an unlikely source; they don’t like to say the “plain k” sound. (And anyways they use their own roots, quite different from kʰíyəp, to express ‘dark; night’.)
The Lower Chinookan languages tend to just use the same root as our familiar Chinuk Wawa púlakʰli ‘night; dark’. But in Kathlamet I found the somewhat similar x̣áp[-]ix̣ ‘at dark’ (which seems to refer to dusk as opposed to night). There’s another, quite different Kathlamet word for this as well, tsúyust[-]ix̣, which helps us to understand that there’s a suffix –ix̣ involved here.
But it’s in Clackamas Upper Chinookan that we find the best match for the GR CW word: gíb[-]ix ‘it was dark’, as well as such forms as da[-]gáp[-]gap ‘a heavy dark fog; thick dark smoke’ and x̣áp/x̣áb ‘dark’. These may all be variations on the same root, in fact.
In Upper Chinookan, Kiksht too has x̣áp/x̣áb ‘dark’, but I don’t find a match for kʰíyəp there.
So Clackamas — a fairly important language in the early Grand Ronde Reservation community — looks to be the most likely source of Grand Ronde CW kʰíyəp, with its gíb —
— which is (from a linguist’s point of view on the facts of Chinookan languages) virtually identical with *kíp*, and I hope you can see the resemblance there with kʰíyəp.
It’s worth reflecting on why an Upper Chinookan word came into the Jargon.
In the earliest known years of Jargon’s existence, you had almost exclusively Lower Chinookan contributing words, because the action was mostly in Clatsop, Shoalwater, and Kathlamet territory.
But later on, once the Grand Ronde rez was founded, its Upper Chinookan community members had a more prominent role than they’d had in the previous cultural mix.