ine-pro

Sometimes, the suffix of a particular PIE descendant's word is not really traceable to a known PIE suffix. While we do know a fair bit about PIE morphology, we (as in, the worldwide linguistic community) are still learning more as we go and figure out things.

We could give the known suffixes names, but it's not always easy to think of appropriate ones. Both *-tis and *-tus are action nouns, but I'm not aware of a distinction in use or meaning between them, so all we can do is call both "action noun". Likewise, *-nós and *-tós are pretty much interchangeable in function (in Germanic and Slavic, obviously so), and I wouldn't know what to call them either. They tended to become past participles in the later languages, but they were not participles in PIE as they were suffixed only to roots, not to verb stems. They could also have meanings that would not be appropriate for a simple past participle.