Learn German: Viele Wagnisse sind heute fast vergessen. - Many ventures are almost forgotten today.

The singular is das Wagnis. Abstract nouns ending in the suffix -nis form their plural by doubling the s and adding -e, resulting in -nisse. You will see this predictable pattern in many other B2-level words, like das Ergebnis becoming die Ergebnisse.

Are all words ending in the -nis suffix neuter like das Wagnis?

Most of them are neuter (das Geheimnis, das Verständnis), but a few common ones are feminine, such as die Erlaubnis (the permission) or die Erkenntnis (the realization). Fortunately, regardless of whether they are neuter or feminine, the plural ending is always exactly the same: -nisse.

What verb is das Wagnis based on?

It comes from the verb wagen, which means 'to dare' or 'to risk'. The suffix -nis is often added to verbs to create abstract nouns that represent the result or act of that verb, making das Wagnis mean 'the venture' or 'the risk'.

Why does the sentence use sind ... vergessen? Doesn't the verb vergessen use haben in the past tense?