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.

Form of -tus appended to nouns

Source: wiktionary.org