The Meaning of Ummi 

Allah said,

وَمِنْهُمْ أُمِّيُّونَ
 
 

And there are among them Ummyyun people,

meaning, among the People of the Book, as Mujahid stated.

Abu Al-Aliyah, Ar-Rabi, Qatadah, Ibrahim An-Nakhai and others said, 
Ummyyun, is plural for Ummi, that is, a person who does not write.

This meaning is clarified by Allah's statement,
 
لَا يَعْلَمُونَ الْكِتَابَ

Who know not the Book,

meaning, are they not aware of what is in it.
Ummi was one of the descriptions of the Prophet because he was unlettered. For instance, Allah said,

وَمَا كُنتَ تَتْلُو مِن قَبْلِهِ مِن كِتَـبٍ وَلَا تَخُطُّهُ بِيَمِينِكَ إِذاً لاَّرْتَـبَ الْمُبْطِلُونَ

Neither did you (O Muhammad) read any book before it (this Qur'an) nor did you write any book (whatsoever) with your right hand. In that case, indeed, the followers of falsehood might have doubted. (29:48)

Also, the Prophet said,

إِنَّا أُمَّةٌ أُمِّيَّةٌ لَا نَكْتُبُ وَلَا نَحْسِبُ الشَّهْرُ هكَذَا وَهكَذَا وَهكَذَا

We are an Ummi nation, neither writing nor calculating. The (lunar) month is like this, this and this (i.e. thirty or twenty-nine days).

This Hadith stated that Muslims do not need to rely on books, or calculations to decide the timings of their acts of worship.

Allah also said,

هُوَ الَّذِى بَعَثَ فِى الاُمِّيِّينَ رَسُولاً مِّنْهُمْ

He it is Who sent among the Ummiyyin ones a Messenger (Muhammad) from among themselves. (62:2)
The Explanation of Amani 

Allah's statement,
 
إِلاَّ أَمَانِيَّ

But they trust upon Amani,

Ad-Dahhak said that Ibn Abbas said that the Ayah means,

"It is just a false statement that they utter with their tongues."

It was also said that;
Amani means `wishes and hopes'.

Mujahid commented,

"Allah described the Ummiyyin as not understanding any of the Book that Allah sent down to Musa, yet they create lies and falsehood."

Therefore, the word Amani mentioned here refers to lying and falsehood.

Allah's statement,
 
وَإِنْ هُمْ إِلاَّ يَظُنُّونَ
 
 

And they but guess, means,

Mujahid said that Allah's statement means,

"They lie."

Qatadah, Abu Al-Aliyah and Ar-Rabi said that it means,

"They have evil false ideas about Allah."
Woe unto Those Criminals among the Jews 

Allah said