CLC Stage 21 - Adjectives to adverbs. Adjectives that end in -US (like laetUS or laetissimUS) can become Adverbs by dropping the -us and adding -ē (just like we add -ly to make adverbs in English). Tools Activity created by: Ginny Lindzey This activity was created by a Quia Web subscriber. To learn how to make your own, just like this, click here.