The spelling of the word "most purposing" can be a bit confusing as it is not commonly used. However, its pronunciation is quite straightforward when using the International Phonetic Alphabet (IPA) transcription. The first syllable is pronounced /moʊst/, similar to the word "most," while the second syllable is pronounced /ˈpɜːrpəsɪŋ/, which is like "purposing" with the stress on the second syllable. Altogether, "most purposing" means the act of having the greatest intention or aim towards a particular goal.
The phrase most purposing does not have a standard etymology as it is not commonly used in the English language. It appears to be a combination of the adjective most and the present participle form of the verb purpose, but the result is grammatically incorrect and not in common usage. The word purpose itself comes from the Latin noun propositum, which means intention or objective.