Necro- is a prefix relating to death and the dead, hence necrophilia, necropolis, necrosis (the dying of flesh) and necromancer (one who communicates with the dead).
Name-inspiration topics must be two-a-penny in OWF's databases by now, despite still not having covered all original Oddworld words.
I would like to know where OWI got the name for the Mongo River from, though. Is it a corruption of Congo, or is it named after the actual River Mongo?
EDIT: Wikipedia seems to sum up the richness and diversity of the word Mongo pretty well:-
http://en.wikipedia.org/wiki/Mongo