<crossing my fingers that all these links work>
The issue about what to call the thing used with an overhead projector does keep coming up, most recently in this New Entry thread:http://forum.leo.org/cgi-bin/dict/forum.cgi?a...
'Overhead transparency' sounds a bit redundant to me, the kind of thing you use in writing when you have to describe the thing as exactly as possible, but don't normally actually say when the context of an overhead projector is clear. However, I could support it as another option.
I'm not familiar with 'overhead' alone in this sense -- in AE, it would more likely be short for the projector, not the transparency. In another thread Martin --cal mentioned using 'slide' colloquially, which I could support adding (from the perspective of the audience, or what shows on the screen).
There's a link to an older forum discussion next to a couple of the existing entries for 'Folie,' but the f-link didn't work for me. I just got a never-ending hourglass icon and could not even get the target URL to show on mouseover, so I can only guess that it may have been this thread 'Folie (Präsentation Powerpoint)' http://forum.leo.org/cgi-bin/dict/forum.cgi?a...
which seems to be a broken link (1-1-70).
But there have been various previous discussions:http://forum.leo.org/archiv.ende/f/folie.html
In this thread,related discussion
Selkie was the only AE speaker who seemed to have heard 'acetate' used for overhead transparencies. In contrast, 'transparency' does seem to be used in BE, judging by comments from Joe W and others. So I would suggest marking 'acetate sheet' as (chiefly) BE, unless other AE speakers have heard of it.
In this one, http://forum.leo.org/archiv.ende/2004_10/04/2...
Norbert thought he remembered having heard 'foil' in AE for overhead transparencies, but, as I pointed out over a year ago (above), he then cited only a few examples from .uk sites, and no dictionary definitions. So I'm still just wondering if those web examples might have been largely foreign students at UK universities or something -- that is, whether they're enough to count, in the judgment of BE speakers.
Andreas's original comment in that thread that
>>"foil" ist doch aber wohl immer etwas metallisches (z.B. Alufolie).
is still exactly how I understand it as well. Ghol agreed in that thread, and Dave UK and Nicole <UK> in this thread, so it would seem to be largely true for BE as well. There have been other supporting comments from an Alan A., a Sarah, and from Mary <NZ>.
And as far as I can tell from reviewing the threads I can open, we don't seem to have heard from any native English speaker in the forum who has ever encountered 'foil' in the sense of an overhead transparency -- or anything else plastic for that matter.
There may be people somewhere who use 'foil' (or for that matter, 'viewfoil,' which sounds equally wrong to me) in the sense of plastic. But if 'foil' is allowed to stay in LEO in any non-metallic sense (and especially as long as the dictionary search doesn't find forum discussions, and the f-link doesn't work), I'm afraid most English speakers will think it's just a flagrant false friend and an error in the dictionary, and many German speakers will be tempted to use it wrongly.