Answer:
ceremonious
Step-by-step explanation:
"ous" is an adjective suffix used in English language to qualify, modify or describe a noun. Therefore, it is mainly affixed to the end of a noun. Some examples of adjective suffix are ness (kindness), ive (expensive), able (manageable), ful (beautiful), ous (poisonous), ic (comic), ary (secondary) etc.
Hence, if something has the qualities of poison, then it is poisonous. Similarly, if something has qualities of a ceremony, it is ceremonious.
In English language, "ous" is an adjective suffix that is typically used to describe something that has a particular quality.