Correct spelling for the English word "poissant" is [pˈɔ͡ɪsənt], [pˈɔɪsənt], [p_ˈɔɪ_s_ə_n_t] (IPA phonetic alphabet).
The word "poissant" does not have an etymology as it appears to be a misspelling or a misinterpretation of the word "puissant".
"Puissant" is an adjective of Old French origin meaning "powerful" or "mighty". It comes from the Latin word "potens" meaning "able, powerful". Over time, the word evolved in Middle English and entered the English language with the same meaning.
However, it is important to note that "poissant" is not a recognized English word and might be a typographical error.