I've noticed, especially in the Horus Heresy books, that the old medieval names for armour pieces are being applied to Astartes armour.
For example, in Fulgrim (P143) the Phoenician is described as wearing a shishak helmet with a lamellar aventail (
This is actually a type of helmet worn by medieval Saracens that was onion dome shaped, had a visor with two eye-holes, a mail of squarish plates (lamellar) that hung from the helmet like a protective cowl (aventail).
So I decided to knock up some pics of SM armour with the parts labelled with the names for the bits. There is a chance of some errors in the labelling as I had to go off What descriptions and names I could find.
As you can see, some pieces have more than one name, so I underlined the name whose description seemed to best fit that particular piece of armour.