As-salaamu ‘alaykum warahmatullaahi wabarakaatuh,
In the arabic language, not a stone is left unturned. The language is so rich that even a concept like tanween has more to it than simply being a nunation attached to nouns. The arabs have divided tanween into four types. One type is known as Tanweenul ‘Iwad and its purpose is to subsititute the tanween for a letter, a word, a sentence or even an attribute!
For example, Allaah (exalted and glorified be he) says:
فَلَوْلَا إِذَا بَلَغَتِ الْحُلْقُومَ
Then why do you not (intervene) when (the soul of the dying person) reaches the throat? 
And he (exalted and glorified be he) continues to say:
وَأَنتُمْ حِينَئِذٍ تَنظُرُونَ
And you at the moment are looking on .
And instead of repeating part of the previous ayah, the tanween attached to 7eena is a substitute for ‘idha balaghatil hulqoom’ so the ayah actually means ‘You at that moment, [when (the soul of the dying person) reaches the throat] you’re looking”
In another ayah Allaah (exalted and glorified be he) says:
…thunder and lightning…
The tanween on ra’d and barq are omitted for “…Ra’dun qassifun wa barqun khatifun…” (Crashing thunder and flashing lightning).
And in another ayah Allaah (exalted and glorified be he) says:
يَوْمَئِذٍ تُحَدِّثُ أَخْبَارَهَا
That day it will declare its information .
And so when this ayah was revealed, the Messenger of Allaah (sallaallaahu ‘alayhi wa salam) said:
فَإِنَّ أَخْبَارَهَا أَنْ تَشْهَدَ عَلَى كُلِّ عَبْدٍ وَأَمَةٍ بِمَا عَمِلَ عَلَى ظَهْرِهَا أَنْ تَقُولَ: عَمِلَ كَذَا وَكَذَا يَوْمَ كَذَا وَكَذَا، فَهَذِهِ أَخْبَارُهَا
Verily, its information is that it will testify against every male and female servant, about what they did upon its surface. It will say that he did such and such on such and such day. So this is its information.” 
Subhanallaah, May Allaah grant us understanding of the Qur’aan, ameen.
 Tafseer Ibn Katheer