Correct spelling for the English word "most infestive" is [mˈə͡ʊst ɪnfˈɛstɪv], [mˈəʊst ɪnfˈɛstɪv], [m_ˈəʊ_s_t ɪ_n_f_ˈɛ_s_t_ɪ_v] (IPA phonetic alphabet).
The phrase "most infestive" appears to be a combination of two separate words or concepts.
1. "Most" is a superlative form of the word "more" and is used to indicate the highest degree or extent of something.
2. "Infestive" is a term that does not seem to have a widely recognized traditional etymology. It appears to be a blend of the words "infectious" and "festive", combining elements of both concepts.
However, it is worth noting that "infestive" is not a standard English word, and it is possible that it was created as a portmanteau or as a coined term to convey a specific meaning.