<u>The fourth principal part, as the perfect passive participle, is an adjective. Usually just the masculine nominative singular is given. The complete forms are: -us, -a, -um.
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<u>N.B.: intransitive verbs do not have a regular 4th principal part (because they can’t be made passive); this includes the verbs that take a dative (noceō, pāreō, etc.)
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<u> Some are listed as –tum/-sum, which is the supine.
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<u> Some have forms in -tūrus/-sūrus (e.g. sum – futūrus; veniō – ventūrus; fugiō – fugitūrus), which is the future active participle
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<u> Some have no fourth form: (e.g. timeō – –; noceō —)
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No, that is not an onomatopoeia. That's more personification. Onomatopoeias are usually the sound the object makes. For example, "buzz!" is an onomatopoeia of a bee or a bug. You could phrase your sentence like this instead: "Crash!! The meteoroids slammed against the earth's surface." In this sentence, "crash!" would be the onomatopoeia.
