Shirk which is associating other gods with Allah is the worst condition of unbelief among in Muhammaddan Islam.
It means literally Association/Partnership of other gods or other non divine beings with Allah and according them the worship and honour that are due to Allah alone and no other.
This word appears in South Arabian writings of the Sabeans as sh-r-k with the connotation of Polytheism.
In Muhammadan Islam, this is the worst spiritual condition of all and the most abhorrent.
*** This is of course, yet again, a COPYand/or a reflection of theBiblicalinjunctions where in theGodof Israel would not tolerate any other rivals in the religion of theIsraelites
Exodus 20: 3 " You shall have no other gods before me"
Exodus 34: 14 " You shall worship no other god..."
Deuteronomy 4: 35 " To you it was shown, that you might know that the Lord is God, there is no other beside him"
Deuteronomy 5 : 7 " You shall have no other gods before me"
There is not a single relevant, intellectual, spiritual and new CONCEPT, PRECEPT, THOUGHT or IDEA in the whole of the Quran that has not been PLAGIARIZED, PLUNDERED, PIRATED and or PERVERTED from theBible and Hebrew Scriptures***