Sill or cill is a supporting rail as in the bottom rail of a window or door (threshold). It's also the name of the base beam on which timber framed houses are built.
But most people also use the term erroneously to refer to the board that closes the bottm of the window opening internally.
It would be more correctto refer to the outside lip if the window is of the type that has one as a sill is also a ledge in geology. (Or a seam with that tendency, I think.)
The English word for a piece of wood (or similar) at the base of a window or door is 'sill'. If there is a technical* word 'cill' that has a different meaning (but same sound) and still relating to material at the base of a window then I'd question the sanity of whoever coined that word. A simpler explanation is that some builders cannot spell.
*I'm assuming that the (putative) technical word was coined within the last 1500 years. I'm open to more persuasive explanations. ;-)Google shows 75,000 hits for window cill and 4.970,000 for window sill which shows most people understand no matter how its spelt unless you are Alan Argument
It's not clear who you are responding to as you aren't using the quoting capabilities of Usenet. If it's me then you should have noticed that I was responding to: "Just for everybodies (sic) reference, it's cill. LOL"
As 'cill' is either a misspelling of 'sill', a long established alternative spelling (but without evidence, or a word for something different.
I see an alternative possibility:
Houseowner: ...and the new window will want a sill of course. Builder's contract: including a cill Houseowner: But where is the stout beam that you agreed to provide? What is holding the window up? Builder: We promised no beam. Houseowner: What about the sill? Builder: A cill is a tatty piece of wood that we stick on the outside of the window frame. Don't know why we bother. There's no beam there. Houseowner: So what's holding the window up? Builder: God knows. Just don't clean the window too vigorously.
They're not MDF, or at least not the same interior-only grade of MDF that's usually known as "MDF". They're more likely to be a cement-bound wood fibre board, like Versapanel. Some of these uses also have fire resistance requirements that the cement boards meet and plain MDF wouldn't.
The message from "Weatherlawyer" contains these words:
Yes.
No. That is a perfectly proper and well established use of the word.
Sill has a number of distinct meanings two of which are the outside window ledge and a horizontal igneous intrusion but they do not disqualify the other legitimate uses of the word.
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