When I was an architectural technician, I used the spelling cill (e.g. window cill). I knew of one architect who used sill and stated that this was the older and more correct form.
My Concise Oxford Dictionary gives both but is weighted more towards sill.
Which version is the more accepted?

  • I'm sure we're about to get 'the definitive answer' from those who 'just know', or more probably conflicting ones. Try raw Google counts for "window sill", "painted the cill" etc. Also, do comparisons on Google Ngrams. This won't give ' the answer', but will give you a feel for what to take on board. – Edwin Ashworth Feb 13 '14 at 11:33
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    As a non-native speaker who has absorbed English extensively for 4 decades, I can tell you that this is the first use of cill I have ever seen and even my spell checker baulks at it – mplungjan Feb 13 '14 at 12:39
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    As a native speaker, it is also the first time I have seen "cill". – nxx Feb 13 '14 at 14:56
  • I think the spelling cill has something to do with spandrels. I used to work in a design school in London, and I do remember something about this. I'll look around and see if I can find more information. – Tucker May 7 '14 at 10:06

In greater use? Sill.

Middle English sille, from Old English syll; akin to Old High German swelli beam, threshold First Known Use: before 12th century

This Google Ngram shows sill as being in greater use than cill.

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Which is correct?

Both. They're both attested and have been used in perfectly good English.

Which should you use? Almost certainly sill because it's better-known, while cill is rare enough that some may not recognise it, or think it incorrect even though it isn't.

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The full Oxford English Dictionary includes "cill" only as a historical variant spelling in the entry for "sill". Specifically, the entry's variant forms section includes "18 cill", meaning that they're only aware of it being used in the 1800s (as distinct from "18- cill", meaning 1800s to present).

As such, I would recommend using "sill"; both are correct but "cill" is seldom used in current English – add me to the list of native speakers who can't recall having seen it before.

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  • It appears that the frame at the bottom of the door of a canal lock is referred to as a "cill". I came across this on a sign recently, so you can now subtract me from the list of native speakers who've not seen the term "in the wild"! – David Richerby Mar 11 '14 at 16:42
  • As a matter of fact, I came to this site having Googled this question, as I am building a website for a manufacturer of double glazed windows, and needed to check his spelling. Your answer fits exactly with this particular peculiarity I just encountered. – GeoffAtkins Jan 31 '17 at 16:53

When I was at technical college in England in the 1970s, the ex-tradesmen/lecturers used the spelling cill which seems to tie in with the references here (window cill, cill of lock gate) to the use of cill as a technical term among professionals like builders, architects or engineers and the sill form among the general population.

This also explains the wide difference in frequency; there are fewer professionals than the general population. Hence the mere frequency of a word is not supportive of any arguments about correctness; however, the argument about wanting to APPEAR correct should be modified to match the audience for which one is writing; professional or general.

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  • I can confirm that (in 2019) builders, structural engineers, etc. (in London at least) still in my experience use the spelling 'cill'. – Sam Dutton Feb 7 '19 at 10:39

While at college in the 1970's we were taught cill by our lecturer and that is how I have always spelt it for windows etc. I have taught in a college for 18 years and that is the spelling I teach.

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  • Welcome to EL&U. You may be unfamiliar with Stack Exchange; this is a Q&A site, not a discussion forum, and this answer has already been provided in a more comprehensive manner. I invite you to take the site tour and visit the help center for additional guidance. – choster May 7 '14 at 15:42
  • @choster I know this reply is nearly five years old, but I think you were a bit hard on @ pete! The question was 'Which version is the more accepted?' and @ pete provided information that went beyond the other replies: an example of how the spelling was taught in the past, and how the spelling is taught now. – Sam Dutton Feb 7 '19 at 10:47

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