I was wondering whether a turtleneck is the strict equivalent of a poloneck? I seem to have a vague recollection when I was younger that a turtleneck in the UK was slightly lower and the turnover was sewn together, as opposed to you actually rolling it over yourself, but I may be wrong and things may have changed.The trick here is that both AmE and BrE have the term turtle(-)neck, but it means something slightly different in the two dialects. Turtleneck was originally AmE, and, like many compounds, it is these days more likely in BrE than in AmE to have a hyphen or be spelt as two words. AmE turtleneck is a close, high neck of a garment that is typically folded over (although when I was a teen, the [orig. and chiefly AmE] preppy fashion was to not fold, but to let them appear squashed under the chin). In BrE, such a thing is called polo-neck. So, AmE turtleneck = BrE polo-neck. But BrE turtle-neck is (according to the OED):
A close-fitting roll or band collar, now usu. one intermediate in height between a crew-neck and a polo-neck; formerly also = polo-neck.So, BrE turtle-neck is sometimes used to refer to things that I'd call roll-neck in AmE, and sometimes to things that I'd call (AmE) mock turtlenecks (photo here). But roll-neck seems to provide other problems--which may be dialectal, or just idiolectal (individual). I'd only use it for something that has a neck that has no border (knitters will have to remind me what to call these things)--it's just knit-purled and finished off, and because there's nothing to stop it doing so, it rolls tightly in on itself--as in this photo. But a lot of people seem to be using it to mean a thicker, looser (but not really loose) turtle/polo-neck (not quite a cowl-neck--see below).
Now, I expect that lots of BrE speakers* will comment that they use polo-neck for any of these things--and the OED definition covers that possibility. It may also be the case that the omnipresence of US chain retailers may have also more recently re-introduced the AmE meaning for turtleneck. I don't imagine that one hears polo-neck much in AmE for high necklines, though. When I first heard it here, it misled me, since I assumed that a polo-neck would surely be the type of collar that one would find on a polo shirt--a term that is found in both AmE and BrE for meaning (a) below, but with an additional meaning (b) in BrE:
polo shirt n. (a) a shirt of the kind worn by polo players; (hence) a short-sleeved casual shirt with a collar and buttons at the neck. (b) a shirt with a polo neck. (OED 2007 draft entry)Finally, while the OED doesn't record it (yet), the term cowl-neck describes necklines that are tall and folded-over like a turtle/polo-neck, but which are wide enough that they flop over, rather than covering the neck closely. Now, although I can find cowl-necks on UK sites nowadays, I don't know how far back this term goes in BrE, since it is in AmE dictionaries (Merriam-Webster, American Heritage), but not in the Oxford ones (I'm not at the office with my bigger dictionary collection). So, BrE-speaking women who wore floppy high-necked jumpers/sweaters in the 1970s, what did you call them?
*Don't forget that no one can hear your accent when you type a comment. It's helpful if you always identify your dialect or homeland, or else comments like "well, I always say xyz" aren't very enlightening! (I may have come to know where you're from, but occasional readers won't have.)