The correct spelling of the word "most brickwall" is actually "unstoppable." The confusion may arise from the pronunciation, where the "s" sound in "unstoppable" is often pronounced like a "z" sound. In IPA phonetic transcription, the word would be transcribed as /ʌnˈstɒpəbəl/. It is important to pay attention to both the pronunciation and spelling of words to avoid misunderstandings and miscommunication.
The term "most brickwall" is not a common expression or word, and therefore there is no specific etymology associated with it. It is possible that this phrase is a combination of two words, "most" and "brickwall", but this is purely speculative. It is important to note that without further information or context, it is difficult to determine the exact meaning or origin of this phrase.