There are plenty of synonyms that can be used in place of the word "joined". One alternative is "united", which implies the coming together of separate entities to form one cohesive whole. Another option is "attached", which can refer to physically connecting two things or linking them together figuratively. "Collaborated" is another possibility, which indicates a cooperative effort between individuals or groups. Similarly, "coalesced" can be used to describe the merging of two or more entities. "Conjoined" is also a synonym for joined, and suggests a more permanent or lasting connection. Lastly, "interlocked" implies a mutual dependence or interconnectedness between two things.