This was a pointless answer on ‘Pointless’ (obviously) last week (they had to come up with words ending in ‘nx’ – who says daytime telly rots your brain?). A quincunx is a geometric pattern made up of four points forming a square or rectangle, with a fifth in the middle. If you’re having trouble visualising that, it’s basically the five-side on a dice (yes, yes, I know the singular is ‘die’, but saying that just makes you sound like a wanker – like those people who insist on saying ‘panino’ because ‘panini’ is plural), or the five of anything in a pack of cards.
The word comes from the name of a Roman coin which dates back to ye olde time of 211–200BC. It was worth five twelfths (‘quinque’ and ‘uncia’) of an ‘as’, which (according to my usual in-depth Wikipedia-based research) was the standard Roman bronze coin. Five dots on it showed it was a quincunx, which is why we now use it to describe that formation.
Later, people started using the word ‘quincux’ in English for other things placed in this cross-shape. Quincunxes actually turn up a lot in different places – for example, a quincunx is the standard pattern for planting in an orchard (I don’t know why, and finding out involved reading a different Wikipedia page which, frankly, I couldn’t be bothered to do). They’re also used in modern computer graphics as a pattern for multisample anti-aliasing, and in numerical analysis to describe the two-dimensional five-point stencil, a sampling pattern used to derive finite difference approximations to derivatives. Obviously we all know what those are, so I won’t bore you with the details. Oh, and Thomas Edison of lightbulb-inventing fame had a quincunx tattoo on his forearm. Rock and roll.