Final answer:
The Latin suffix -um is used to form neuter nouns in Latin.
Step-by-step explanation:
The Latin suffix -um is not commonly used in English. However, in Latin, it was used to form neuter nouns, which were neither masculine nor feminine. These nouns were often used to denote objects, substances, or abstract concepts. For example, the Latin word forum (meaning marketplace) became forum in English, retaining the -um suffix.