Eitr can be found on the Weyland Industries table of elements, its a mythical substance in Norse mythology. Believed to be the origin of all living things: the first giant Ymir was conceived from eitr. The substance is supposed to be very poisonous and is also produced by Jörmungandr (the Midgard serpent) and other serpents.
Which makes a lot of sense for Chemical A03959x.91-15 to be the same substance, after all they are giants and the chestbursters are very much like serpents.
The word is used in common Scandinavian folklore as a synonym for snake poison.
In Vafþrúðnismál Odin asks the Giant Vafþrúðnir about the origin of Ymir. Vafþrúðnir answers:
Ór Élivagomstukko eitrdropar,svá óx, unz varð ór iötunn;þar órar ættirkómu allar saman,því er þat æ allt til atalt.
Eitr drops splashed
that grew into a giant
who begat all families
from which all [giants] come
that is why we are easily angered
The last line of the stanza in Vafþrúðnismál
where Vafþrúðnir says “that is why we are easily angered”, is a word-play with the meaning of the word eitr, as it also means anger/angry (similar to “poison a relationship”).
Giant Furious Gods, that’s pretty much the summary of it.