I'm asking about the literal meaning behind the word, its etymology, etc.
Welhelm Gesenius suggests in his Hebrew Dictionary of Tanach that the word derives from the Coptic saht (woven) + nuje (false). He also notes the Septuagent's rendering κίβδηλος (spurious). A pdf of the dictionary page can be found here.
Ibn Ezra already notes in his commentary to Vayikra 19:19 that the word is a dis legomenon and as such we can't know for sure what its exact meaning is other than that of linsey-woolsey which is given in the verse itself (Devarim 22:11):
לֹא תִלְבַּשׁ שַׁעַטְנֵז, צֶמֶר וּפִשְׁתִּים יַחְדָּו
Do not wear Sha'atnez, wool and linen together.