HL Mencken in American Speech IV, 1929, surmised that the teddy was so called “from its real or fancied resemblance in general shape (or shapelessness) to the teddy-bear.”. Not sure I see it myself but there’s no better suggestion on offer.
Earliest cite in OED for the female undergarment is 1924; teddy-bear goes back to 1907.
Ah, this reminds me, years ago on an annual shopping trip with a friend…
We’re in Victoria’s Secret buying something for my wife, and there’s a couple in the store obviously having a fight, with the woman white-hot angry and the man trying to placate her. She’s in line ahead of us and he wanders off for a while, and then he comes back with a cute little pink stuffed bear, which he hands to her.
“What’s this?” she asks suspiciously.
“You said we wanted to get her a teddy,” he says, in an I was just trying to help voice, and unfortunately my friend and I can’t help ourselves and we burst out laughing.
She gave us one good look and we stopped, though. :eek: