The phrase "most by-the-way" is not a single word, but rather an expression that means something that is said casually or incidentally. Antonyms for this phrase could include words that suggest focused or intentional communication, such as "main point," "purposefully," or "consciously." Other antonyms might suggest deliberate or upfront disclosure, such as "straightforward," "transparent," or "candid." Words like "central," "core," or "primary" might also be considered antonyms, as they suggest a strong and essential focus on something important, rather than a casual or tangential comment. Ultimately, the antonyms for "most by-the-way" depend on the context and intent of the communication.