The Greek word ΙΛΥΣ, written ilus in latin characters, means "mud".
My question is:
Does this word appear anywhere in the Spanish literature?
No, it doesn't
I have looked for the word in the CORDE and in old dictionaries, but every reference I find to "Ilus" is to a king of Troy. This is attested in the Terreros y Pando dictionary from 1787:
ILUS, ó ILO, cuarto Rei de Troya, hijo de Tros, ó Trois, y de la Ninfa Calirhoe, y que fabricó la Ciudadela de Troya, y echó á Tantalo de su Reino.
This is written in a book from the beginning of the 15th century:
[...] del rey trous nascio ilus que fizo la mayor fortaleza de troya [...].
Spanish words for mud include barro and lodo.
You can find also some cases of "Ilus." as the abbreviation for Ilustración.