It's time for an ancient Greek lesson.
The endings -ων, -ουσα, -ον are the ancient endings of present participles in the active voice, eg: λύων, πράττων, etc. In modern Greek, such participles end in -οντας or -ώντας, eg: λύνοντας, πράττοντας. But unlike the ancient participles, they are not declined.
The modern ending -οντας/-ώντας is the same (or almost the same) as the ancient ending for the accusative plural of the masculine form of such participles. Eg:
- (ὁ λύων ->) τοὺς λύοντας -> λύνοντας
- (ὁ διδοὺς ->) τοὺς διδόντας -> δίνοντας
Some ancient participles have survived over the centuries and are now used as adjectives, present participles or even nouns. Words like ενδιαφέρων, απών, παρών and επιβλέπων have derived this way.
PS: There are some ancient Greek adjectives ending in -ων, -ουσα, -ον or even in -ων, -ων, -ον, but in most cases, these endings denote a participle.
I hope this helps. :-)