I wrote before on the Qur'anic word "jahannam" (hell) in a post about those who shouted "Ila Jahannam" to Saddam at the time of his execution. Let me correct myself. Jahannam is of old Hebrew origin, another word for hell in the Qur'an (jahim) is of old Ethiopic origin. Ibn Mandhur in Lisan Al-`Arab notes that Jahannam is of `ajami (non-Arabic) origin and thinks that the fact that is never preceded by Al At-Ta`rif as evidence. But even Ibn Mandhur notes that some Arab linguists believe that Jahannam is of old Arabic origin from a word that means "of the deep bottom". And two of the seven names of hell in the Qur'an are of Syriac origin: "sa'ir" and "saqar." Saqar is least known and least used today. But it appears some 5 times in the Qur'an, as in:

سَأُصْلِيهِ سَقَرَ {26}

وَمَا أَدْرَاكَ مَا سَقَرُ {27}

لَا تُبْقِي وَلَا تَذَرُ {28}

لَوَّاحَةٌ لِّلْبَشَرِ {29}

عَلَيْهَا تِسْعَةَ عَشَرَ {30}

(I don't have time to translate, especially the interesting reference to the number 19 in the last ayat but avoid the apologetic and inaccurate translation of Yusuf Ali, which is the most widely used translation by Muslims here in the US. When I used to read that Surah as a kid, that section scared me.)