الناموسية فوق كيس النوم في الخيمة.

Because Arabic often leaves out the present-tense to be in simple statements.

So a sentence like this is a nominal sentence:

• الناموسية = the subject/topic
• فوق كيس النوم في الخيمة = the predicate, telling you where it is

In other words, Arabic naturally says something like:

• The mosquito net above the sleeping bag in the tent

with the meaning The mosquito net is above the sleeping bag in the tent.

If you wanted was or will be, then Arabic would usually use a verb:

• كانت الناموسية فوق كيس النوم = the mosquito net was above the sleeping bag
• ستكون الناموسية فوق كيس النوم = the mosquito net will be above the sleeping bag

الناموسية means mosquito net.

It comes from ناموس = mosquitoes, and ناموسية refers to the net or covering used against them.

A learner may also notice that it looks feminine, and that is correct:

• it ends in ـة (tāʾ marbūṭa), a common feminine ending
• so if you added an adjective, that adjective would normally be feminine too

For example:

• الناموسية البيضاء = the white mosquito net

This is an example of the iḍāfa construction, often called the construct phrase.

Literally, كيس النوم is:

• كيس = bag
• النوم = sleep / sleeping

So the phrase means something like bag of sleeping, which is the normal Arabic way to say sleeping bag.

This is very common in Arabic. Instead of stacking nouns the way English does, Arabic often links them in an iḍāfa:

• باب البيت = the door of the house
• كتاب الطالب = the student’s book
• كيس النوم = sleeping bag

Because in an iḍāfa construction, the first noun normally does not take ال.

So:

• كيس النوم is correct
• الكيس النوم is not correct

The first noun, كيس, is made definite by the whole phrase. Since the second noun is definite here (النوم), the whole expression is definite:

• كيس النوم = the sleeping bag

This is an important pattern:

• بيت رجل = a man’s house / a house of a man
• بيت الرجل = the man’s house

The definiteness of the whole phrase is determined by the second noun.

Yes, this is a very natural question.

• فوق means above, over, or on top of
• على means on, often with a stronger sense of contact or support

So the difference is roughly:

• فوق focuses on higher position
• على often suggests direct physical contact

In real usage, the line is not always sharp, and both can sometimes work depending on context.

Here, فوق كيس النوم suggests that the mosquito net is over / above the sleeping bag. That makes good sense, because a mosquito net often hangs over something rather than simply resting on it.

Most naturally, في الخيمة gives the location of the whole scene: the mosquito net is above the sleeping bag, and all of this is in the tent.

So the most natural understanding is:

• the mosquito net is above the sleeping bag
• this is happening in the tent

That said, Arabic word order can sometimes leave a little room for interpretation, just like English can. Context usually makes it clear.

In this sentence, most learners should understand في الخيمة as a normal final location phrase applying to the overall situation.

There are two useful pronunciation points here.

1. Sun-letter assimilation

In:

• الناموسية
• النوم

the letter after الـ is ن, and ن is a sun letter. So the l sound of ال is not pronounced separately.

So you pronounce them roughly as:

• an-nāmūsiyya
• an-nawm

2. No assimilation before خ

In:

• الخيمة

the letter خ is a moon letter, so the l sound is pronounced:

• al-khayma (or al-khaymah in pause)

So the whole sentence is approximately:

• an-nāmūsiyya fawqa kīs an-nawm fī al-khayma

The ending ـة is tāʾ marbūṭa, a very common ending on feminine nouns.

In normal pause pronunciation, you usually say it as -a or -ah:

• الناموسية → an-nāmūsiyya(h)

But in fully inflected formal reading, when a case ending is pronounced, the t sound can reappear:

• الناموسيةُ
• الناموسيةَ
• الناموسيةِ

In everyday learning, it is enough to remember:

• at the end of a phrase, it usually sounds like -a / -ah
• in careful grammar or connected formal reading, it may sound more like -at before the case ending

In fully vowelled formal Arabic, the sentence can be written as:

ٱلنَّامُوسِيَّةُ فَوْقَ كِيسِ ٱلنَّوْمِ فِي ٱلْخَيْمَةِ

Here is why:

• ٱلنَّامُوسِيَّةُ: nominative, because it is the subject/topic of the nominal sentence
• فَوْقَ: an adverb of place, here in the accusative form
• كِيسِ: genitive, because it comes after فوق in this construction
• ٱلنَّوْمِ: genitive, because it is the second term of the iḍāfa
• ٱلْخَيْمَةِ: genitive, because it comes after في

In normal unvowelled Arabic writing, these endings are usually not written, and in everyday pronunciation they are often not fully pronounced either.

Yes, Arabic word order is flexible, but changing it can slightly change the emphasis.

The original sentence is very natural and neutral:

• الناموسية فوق كيس النوم في الخيمة.

If you move the location earlier, you shift the focus:

• في الخيمة الناموسية فوق كيس النوم.

That can sound more like:

• In the tent, the mosquito net is above the sleeping bag

So the original order is a good standard pattern for learners:

• subject first
• then the location phrase

Grammatically, النوم is a noun meaning sleep.

But in an iḍāfa like كيس النوم, Arabic uses that noun where English would often use another noun as an adjective-like modifier:

• sleeping bag
• literally, bag of sleep

So yes, it is still a noun in Arabic, but in translation it corresponds to English sleeping rather than just sleep.

This is a very common difference between English and Arabic word-building.