1. namkum - lightning bolt
2. hu - wind
3. zetop - potion
4. bluon - human
5. namkumi - lightning bolts
6. hui - winds
7. zetopi - potions
8. bluoni - humans
9. kum - light
10. namhu - mighty storm
11. nambluon - ruler, king, queen
12. namtwiN - total conquest
That plural morpheme (it's a morpheme because it adds meaning) is a suffix. We want to be sure we aren't confusing that with any other random [i] which might occur in our data. So, we write the suffix like this: -i.
To show how all the morphemes in the word are arranged, we can write the word with hyphens between its morphemes like this:
hu-i
wind-PL (NB: PL = plural_
Examples 9-12 add some information on the meaning of 'nam-'. This attaches to the root either as a prefix or perhaps as the first part of a compound noun. If we look at the meanings of all these words, we might narrow the possibilities of the meaning of 'nam' to something like 'ruler' or 'top' or 'power'. We can't be sure exactly.
We can write 'nam' as a prefix 'nam-' or as a stand-alone word 'nam'. the hyphen inidcates that you have cause to believe that the form is a bound prefix like pre- or omni-. Without the hyphen, we are indicating that 'nam' can stand alone as its own word. Hyphens indicate necessary conection. So although I could write 'kum' as 'kum-' because it can connect to a plural, it does not have to connect obligatorily to a plural. I can say 'kum' or 'kumi'.
So, if I want to write 'nam'... so far I have only seen that as a prefix. I'd write it as nam- until I have data that it could stand alone as its own word.