What is the meaning of -atus?

-ed. Used to form adjectives from nouns indicating the possession of a thing or feature.

Used to form adjectives from other adjectives, especially color names, with the sense "wearing [adjective](-colored) clothes".

-like, -ate. Used to form adjectives from nouns indicating a resemblance or likeness to the noun.

Added to nouns or adjectives to form nouns denoting a rank or office, a group of officials associated with such a rank or office or a certain state.

Source: wiktionary.org