Nope, not a super-relaxed epic Greek poem (and the award for the most obscure joke ever goes to…). A chiliad is a noun for a group of a thousand things. You can also use it for years – so it’s a somewhat poncy alternative to ‘millennium’ (and also works in that Robbie Williams song, if you sing it slowly). ‘Chiliad’ is actually older than ‘millennium’, and first appeared in the late 1500s, whereas the m-one (I have trouble spelling it, so I’m not typing it again) didn’t turn up in written English until the following century. Unsurprisingly, both words come from other words for ‘thousand’ – ‘chiliad’ from the Greek word ‘chilioi’, and ‘millennium’ (I copied and pasted it that time) from the Latin ‘mille’.
There’s also a thing called ‘chiliasm’, which is nothing to do with orgasms, sorry – it’s a religious belief that before the final judgement, we’ll get a paradise or golden age on Earth (it’s safe to say that doesn’t look like it’s happening any time soon). And if you’re one of those religious people, then you’re ‘chiliastic’.
Sadly, chiliad is actually pronounced with a hard ‘c’ – think ‘cat’ or ‘Cillian Murphy’ (because it’s always nice to think about Cillian Murphy). This obviously makes it less fun, as it no longer sounds like it’s related to ‘chillax’, which is why I’ve left it til the end to tell you that.