Adding the suffix - ous to the word danger forms a/an

verb

adjective

adverb

It forms an adjective. Danger by itself is a noun, if you add the suffix - ous, it makes it an adjective (A dangerous man). The adverb would be if you added - ous + - ly, and make it - dangerously (He drives dangerously). There is no verb "danger" or using any of its derivatives, the only way to make a verb out of danger is to add a prefix - en, and make it - endanger.