Akciğer enfeksiyonu sonunda yatıştı.

No. Here -u is not the accusative ending; it is the 3rd-person possessive ending used in a very common Turkish noun compound pattern: akciğer enfeksiyonu = lung infection.

In this pattern, the first noun names the type (akciğer = lung), and the second noun takes the compound ending (enfeksiyon + u). Compare:

• baş ağrısı = headache
• telefon numarası = phone number

So the whole phrase is one unit, and in this sentence it is the subject, not a direct object.

In Turkish noun compounds, the first noun usually stays singular and functions like a label or category word. So akciğer enfeksiyonu means lung infection, not necessarily an infection of only one lung.

This is similar to English expressions like car door, toothbrush, or lung disease, where the first noun is also singular.

Here sonunda means finally, in the end, or eventually.

It is best learned as a common set expression. Sonda is more literal and usually means something like at the end in a physical or positional sense, such as at the back or in the last place. In this sentence, sonunda is the natural choice because it expresses that something took time and then eventually happened.

It comes from yatışmak, which means to calm down, settle down, or subside.

It is related historically to yatmak, but for learning purposes it is better to treat yatışmak as its own verb with its own meaning. In medical Turkish, it is very natural to say that pain, swelling, inflammation, fever, or an infection yatıştı when it has eased or subsided.

This is the Turkish simple past tense suffix, often shown as -DI because its form changes.

In yatıştı:

• the stem ends in ş, which is a voiceless consonant
• after a voiceless consonant, d becomes t
• vowel harmony makes the vowel ı

So:

yatış- + -DI → yatıştı

Yes, that also works.

Turkish word order is flexible, although the verb usually stays near the end. The original sentence, Akciğer enfeksiyonu sonunda yatıştı, is natural. If you say Sonunda akciğer enfeksiyonu yatıştı, you put a little more emphasis on finally.

Turkish does not use articles like English a/an and the.

So the sentence itself does not explicitly say a lung infection or the lung infection. English has to choose based on context. In many real situations, English would say the lung infection because the speaker and listener already know which infection is being talked about.

The ğ is not pronounced like a hard English g.

In akciğer, it usually just softens the transition and may create a slight y-like glide, so the word sounds roughly like ak-jee-yer rather than ak-gee-er. The important point is: do not pronounce ğ as a strong g sound.