Correct spelling for the English word "preomission" is [pɹɪəmˈɪʃən], [pɹɪəmˈɪʃən], [p_ɹ_ɪ__ə_m_ˈɪ_ʃ_ə_n] (IPA phonetic alphabet).
There is no widely recognized etymology or existing word "preomission" in the English language, at least as of the current knowledge. It is possible that the term you are referring to may be a neologism or a specialized term used in a specific field or context. Without further information, it is difficult to provide a precise etymology for this particular word.