Two nibbles is an acceptable answer.

You say that, but that is (or at least was) a real problem: https://en.wikipedia.org/wiki/Word_(computer_architecture)

You jest, but a byte isn't always 8 bits (well, nowaday it kinda is, de facto, but it wasn't always like that). An 8-bit byte is called an octet, I don't see it used much in english, but apparently it is used nonetheless, after a quick check. Since octets are the standard byte size, I suppose we could call them "metric bytes".