"azat" is the word for noble in Parthian. Azat Cavalry maybe?

400 Parthian Azat's threw an army of 50,000 mounted warriors against Mark Antony in 36 BC. Not all of that 50,000 would lack any sort of armour. We know they used spear and javelin cavalry who had some armour. The "lesser noble" cavalry may not have been able to purchase a full cataphract outfit but that doesn't mean they had to stay at home.