Sub-joins refer to a connection or attachment of one thing to another. There are several synonyms for this word, including affixing, annexing, attaching, appending, joining, and adding. Affixing implies the action of attaching something firmly to something else, whereas annexing denotes adding to something as an extension or addition. Attaching is the process of fastening or fixing one thing to another, whereas appending means adding something to another thing or document. Joining signifies connecting two or more things together, whereas adding implies including a new element to an existing set or group. With these synonyms, one can clearly communicate the action of sub-joining in a variety of contexts.