"The dog collects very many bones."

Translation: Canis plurima ossa colligit.

[commediadellarte]

how would you say just 'many' (not 'very many')?

[Moopish]

You would use a form of multus, multa, multum most likely.

Canis multa ossa colligit. -> The dog collects many bones.

[David514341]

Os (s) 'bone' and Ossa (pl) 'bones' are third declension nueter, and can be Nominative or Accusative forms. In this case, ossa is accusative plural.