"Tied in" is a common phrase used to describe a situation where two or more things or ideas are interconnected or related. However, there are several synonyms that can be used in place of "tied in" to convey the same meaning. Words like "linked," "connected," "associated," "intertwined," "entwined," "interlocked," "interrelated," and "related" can be used interchangeably with "tied in." These words can be used in a variety of contexts, from describing the relationship between different plot points in a story to explaining the connection between different fields of study. Ultimately, these synonyms serve as useful tools for writers looking to add variety and nuance to their language.