I got a general email from a colleague I don’t personally know, which talked about something going ‘skew if’. The most common spelling is skew-whiff, but given that Wikitionary marks the word as ‘Britain, Australia, New Zealand, colloquial’, I’d better explain it for everyone else.
It means askew, lopsided, not straight, not going to plan or not working properly, as in the computer systems which were the subject of the email. Wikipedia explains the origin: “The expression ‘skew weft’ dates at least from the 18th century as a term used by handloom weavers, typically in northern England. It was used originally to describe fabric which was out of alignment, and the term survives today in the manufacture of glass fiber cloth.”
I was originally sceptical of that explanation, but Google shows about 296 occurrences of ‘skew weft’ in the context of weaving. I am still moderately sceptical of that explanation.
Wiktionary gives the alternative spellings skewwhiff, skew whiff, skewiff (which is what I searched for after seeing the colleague’s email) and squewiff. Google Ngrams gives no results for skew whiff and squewiff (and, indeed, skew weft, which is odd, seeing that one of the results of the Google search for skew weft is on Google Books) and shows that skew-whiff is about six times as common as skewiff and skewwhiff. It also shows usage dating from the 1930s, which raises the question of why an obscure and specialised noun phrase from the 18th century suddenly emerged as an adjective in the 1930s. It also also shows that usage is about 10 times as common in British English than in American English.
So did my colleague make a mistake in a work-related email? Yes, but I know that things like this happen when people formally write a word which is more often informally spoken, under pressure (last week was a very busy week for our IT department). I don’t say this word often and, as I mentioned, my first guess at the spelling was skewiff (which is, however, not a mistake).
Meanwhile skew if, is correct in the context of mathematical explanations such as “Two lines are skew if and only if they are not coplanar” (Wikipedia), that is, they are not parallel or intersecting.