There are several synonyms that can be used in place of the word "opon". One of the most common synonyms is "board", which refers to a flat and often rectangular piece of wood or other material that is used for a variety of purposes. Another synonym for "opon" is "surface", which refers to the outer layer or top layer of something, such as a table or a piece of paper. Other possible synonyms include "plank", "tabletop", "desktop", "countertop", and "workbench". However, the exact synonym that is most appropriate will depend on the context in which the word is being used.