A famous rhyming couplet from the Necronomicon, quoted by Lovecraft in his fictional setting of the Cthulhu Mythos.
The english translation from the original Arabic is most often given as:

That is not dead which can eternal lie,
And with strange aeons even death may die.

Transliterated, the Arabic sounds like:

la mayyitan ma qadirun yatabaqa sarmadi
fa itha yaji ash-shuthath al-mautu qad yantahi.

Literally translated, it means:

That is not dead which has the capacity to exist eternally,
And if the abnormal (bizarre, strange) ones (things, times?) come, then death may cease to be.

One Arabic phrase, yaji ash-shuthath, perhaps gives a clue to a deeper mystery. It is plural, and it literally means 'the abnormal', referring to people or to things, depending on the context. Yaqi means 'comes' or 'are coming'. Colloquial Arabic often transforms the soft j-sound into a hard g-sound and many times the vowel endings are left off and the words slurred together, as we often do in English. Therefore a possible rendering of this phrase in colloquial Arabic would be yag-shuthath, with a slight change in the quality of the vowels easily recognisable as Yog-Sothoth. -Information gained from the notes given in Call of Cthulhu 5th edition.