Is every word that ends in -нный a past passive participle?
For example the word сезонный meaning seasonal? It has the double -нн ending that the past passive participles have but for the life of me I can't figure out which verb it comes from....
Another one that has me confused is сельскохозяйственный meaning argicultural. Is this a past passive participle? If so what verb is it made from?
Or are both of these just adjectives with a double -нн ending?
I'm totally confused because I though all words with the -нный endings were past passive participles but in these two cases I can't figure out what verb they would have come from.
Thanks for any help!