Dedecorous is a term that refers to something lacking proper decorum or manners. Synonyms for the word could include inappropriate, impolite, indecorous, indecent, unseemly, and unbecoming. These words all describe behavior or actions that are not considered socially acceptable or appropriate. In some cases, these synonyms may also refer to language or clothing that is not suitable for a certain situation or audience. It is important to be mindful of our words and actions, and to strive for decorum and manners in all aspects of our lives.