Why is ‘plum’ púm in Quinault Salish?
The only dictionary of Quinault, a Southwest Washington Salish (a.k.a. a “Tsamosan”) language, tells us púm means ‘plum’. Huh?

Image credit: Fine Art America
That word looks a little bit like English ‘plum’ — but it sounds mighty different, [púm] versus [pʰlə́m].
So I have doubts that it’s a loan from English.
As usual, we should also consider Chinuk Wawa, when we’re investigating loan words into Pacific NW Indigenous languages.
CW has a more closely matching word, lipúm ‘apple’, from Canadian/Métis French la pomme.
In fact we know of an exact match in the variant CW form < pomme >, according to Father Lionnet on the lower Columbia River. His 1853 vocabulary translates this word as ‘pommier‘ (‘apple tree’).
We might speculate that some Chinook Jargon speakers in previous times treated the word(s) for ‘apple’ / ‘apple tree’ as generic for ‘domesticated fruit’. This is certainly what happens at modern Grand Ronde, where for example a banana is a yułqət-lipum, a ‘long apple’.
Along with that possibility, I expect English to have played an ongoing influential role in the frontier-era and later Quinault community. So the word ‘plum’ itself may have also helped shape the Quinault Salish word púm.
Bonus fact:
In French, ‘plum’ would be (le) prune.
In the Cree-French Métis language Michif, sort of a cousin of Chinook Jargon, that’s li prenn.
Not terribly surprisingly, Michif also has the loan of the English word: enn plum.
