The word "achates" can be difficult to find synonyms for as it is a relatively obscure term. However, there are a few words that can be used in its place depending on the context. For example, "companion" or "friend" can often be used in place of "achates" to describe a close and trusted companion. Alternatively, "ally" or "associate" may be more appropriate if the context refers to a partner or supporter in a particular endeavor. In literature, the term "henchman" can also be used in place of "achates" to refer to a loyal and trusted follower. Ultimately, the choice of synonym will depend on the specific context of the word usage.