"Through and through" is an idiomatic expression that means completely or thoroughly. There are several synonyms that can be used to convey the same meaning, including wholly, entirely, thoroughly, completely, fully, and perfectly. These words can be used in various contexts, such as describing someone who is dedicated to a cause through and through, or a job that has been completed wholly or entirely without any errors. In some cases, adding the adverb "thoroughly" to the sentence can also convey the same meaning as "through and through." It's important to note that while all of these words express completeness, they can also have other connotations depending on the context and tone of the sentence.