[quote=@Jbcool]
Both of them are real Latin; Decurion is a rank in the Legiones Astartes, the other is a name. Where's the confusion?
[/quote]

You mean a lieutenant? That rank is more commonly called Lieutenant. Decurion, by comparison, is less widely used than Pack Leader. Which makes no sense, because in the Roman army it was a term used for cavalry. Then, you give him a name like 'Celer,' the main form in Latin for 'fast,' and it just makes the whole thing sound like a random faux-latin term made up solely for 40k.

Even more confusing, you picked the one term for that rank that's plastered across the internet in association with an entirely different faction.