1. "The plus-size 'bikini'": "Note that the caption refers to the bottoms as 'trunks,' a word that strikes me as way too masculine (perhaps because I associate it with elephant appendages)."
2. "'The Giving Tree' — 'Remember that book...": "In his childhood, the boy enjoys playing with the tree, climbing her trunk, swinging from her branches, and eating her apples. However, as time passes the tree becomes mean, jealous, and stingy...."
When things like that happen around here, it's de rigueur to consult the (unlinkable) Oxford English Dictionary. The first meaning, going back to 1490, is "The main part of something as distinguished from its appendages," which explains how we talk about trees.
1490 Caxton tr. Eneydos iv. 17 Eneas..hewe the troncke of a tree oute of the whiche yssued bloode.That leads to a figurative use, for example:
a1616 Shakespeare Measure for Measure (1623) iii. i. 70 You consenting too't, Would barke your honor from that trunke you beare, And leaue you naked.The second meaning is: "The human body, or that of an animal, without the head, or esp. without the head and limbs, or considered apart from these..."
a1616 Shakespeare Henry VI, Pt. 2 (1623) iv. ix. 84 There [will I] cut off thy most vngracious head;..Leauing thy trunke for Crowes to feed vpon.So how do we get to the elephant's trunk, which seems to have it backwards, with the word referring to the appendage and not the main part? And what about those swimming trunks? There's the "trunk" that is a large piece of luggage, and I see that usage seems to have come from the fact that trunks were once made out of tree trunks. Another word for that sort of trunk is "chest," which seems to take us back to the human torso sort of trunk. A puzzle!
Anyway, the elephant's trunk is the 15th meaning for "trunk," and there's no explanation for why the appendage gets the word that originally meant the main part.
1589 R. Baker in R. Hakluyt Princ. Navigations i. 138 The Elephant..With water fils his troonke right hie and blowes it on the rest.And we need to scroll down to meaning #17 to get to the pants category, first with "trunk-hose," and then "trunks" to mean "Short breeches of silk or other thin material; in theatrical use, often worn over tights...."
1613 S. Purchas Pilgrimage 816 There was another strange creature in Nicaragua..like a blacke Hogge, with..a short truncke or snowt like an Elephant....
1836 Dickens Pickwick Papers (1837) xv. 152 The appearance of Mr. Snodgrass in blue satin trunks and cloak, white silk tights and shoes, and Grecian helmet.And finally, "orig. U.S. Short tight-fitting drawers worn by swimmers and athletes."
1883 Pall Mall Gaz. 26 July 7/1 Captain Webb attempted his perilous feat of swimming the Niagara Rapids... He wore a pair of silk trunks....With little help from the OED, I'm going to leap to the supposition that meaning #17 is an example of metonymy — where a word referring to one thing is used to refer to a related thing, like "dish" for the food on the dish. The trunk is in the garment and the garment gets called by the thing it contains. That wouldn't explain why we say "trunks" in the plural, which is like "pants," which we can easily tell is plural because pants have 2 legs. (Calling pant legs "legs" is clearly metonymy.) Oddly, trunks, unlike pants, lack legs, but I think if we go back to the first #17 usage and see "trunk-hose," we get a clue for where "trunks," plural, came from. It was a one-piece garment, the tights, and the term got transferred to those puffy panties that covered up the dancer's bulges...
1894 Ralph in Harper's Mag. Aug. 341 Nude bathing will not be permitted... The use of tights or ‘trunks’ will not be allowed.
... until they didn't....
As for the elephant's trunk, the 15th meaning of "trunk," I'm thinking the word for the main part became the word for the appendage as way to express the awesome size of the appendage. It might have been a comical figure of speech at one time, the way a man's very large phallus might be called his "third leg."