Termometreyi kullandım; ateşim yüksek değilmiş.

Because termometreyi has the accusative ending.

• termometre = thermometer
• termometreyi = the thermometer

In Turkish, when a direct object is specific/definite, it usually takes the accusative ending. Since the speaker means a particular thermometer they used, -yi is added.

Why -yi?

• the base word ends in a vowel: termometre
• after a final vowel, Turkish inserts a buffer consonant y
• then the accusative vowel appears: -i

So:

• termometre
  • -y-i → termometreyi

Kullandım means I used.

It breaks down like this:

• kullan- = to use
• -dı- = past tense
• -m = I

So:

• kullan-dı-m → kullandım = I used

Because of vowel harmony and consonant voicing, the past tense appears here as -dı.

Because Turkish often leaves out subject pronouns when the verb ending already shows the subject clearly.

In kullandım, the ending -m already means I. So:

• Ben termometreyi kullandım = I used the thermometer
• Termometreyi kullandım = also I used the thermometer

Both are correct, but the second is more natural unless ben needs emphasis.

Ateşim literally means my fire, but in Turkish it is the normal way to say my fever or my temperature in a health context.

It breaks down like this:

• ateş = fire / fever
• -im / -ım / -üm / -um = my

So:

• ateş-im → ateşim = my fever

Turkish often uses possessive suffixes instead of separate words like my.

Yes, ateş literally means fire, but it is also commonly used for fever in Turkish.

This is similar to how English uses temperature-related words metaphorically in health contexts. In Turkish:

• Ateşim var = I have a fever
• Ateşim yüksek = My fever is high / My temperature is high

So in medical or everyday health situations, ateş very naturally means fever.

Because Turkish typically describes fever as high or low, just like English often does.

• yüksek = high
• düşük = low

So:

• Ateşim yüksek = My fever is high
• Ateşim düşük = My temperature is low

Using çok would mean very/much, which does not fit as naturally here.

Because yüksek is an adjective, and Turkish usually negates adjective-based statements with the separate word değil.

Examples:

• yorgun = tired

• yorgun değil = not tired

• yüksek = high
• yüksek değil = not high

So değil works like is not / not for nouns and adjectives.

The -miş ending adds a meaning like:

• apparently
• it turns out
• I learned that
• I found out that
• it seems

So ateşim yüksek değilmiş is not just my fever was not high. It suggests the speaker learned this indirectly or discovered it after checking.

In this sentence, after using the thermometer, the speaker concludes:

• Ateşim yüksek değilmiş = Apparently my fever wasn’t high / It turns out my fever isn’t high after all

This is a very common use of -miş in Turkish.

Because the predicate here is the whole negative expression yüksek değil.

Turkish forms it like this:

• yüksek = high
• değil = not
• değilmiş = apparently not / it turns out not

So the evidential ending goes on değil, because değil is carrying the negation of the predicate.

Compare:

• Ateşim yüksekmiş = Apparently my fever is high
• Ateşim yüksek değilmiş = Apparently my fever is not high

These are different in both tense and information source.

• Ateşim yüksek değil
  = My fever is not high.
  Plain present statement.

• Ateşim yüksek değildi
  = My fever was not high.
  Direct past statement.

• Ateşim yüksek değilmiş
  = Apparently my fever is not/was not high.
  The speaker learned or realized this indirectly, often just now.

In your sentence, değilmiş fits well because the speaker used the thermometer and then found out the result.

It can feel like either isn't after all or wasn't after all, depending on context.

Turkish -miş does not map perfectly onto one English tense. It often expresses reported/discovered information rather than a simple tense equivalent.

So in this sentence, English might translate it as:

• It turns out my fever isn’t high
• Apparently my fever wasn’t high

Both can work depending on the broader situation.

The semicolon links two closely related ideas:

• Termometreyi kullandım = I used the thermometer
• ateşim yüksek değilmiş = it turns out my fever isn’t/wasn’t high

The idea is: first the speaker checked, then they learned the result.

In everyday writing, you might also see:

• Termometreyi kullandım, ateşim yüksek değilmiş.
• Termometreyi kullandım. Ateşim yüksek değilmiş.

The semicolon is just a neat written way to connect the two clauses.

Yes, but it would sound a little different.

• Termometreyi kullandım ve ateşim yüksek değilmiş.

This is grammatical, but ve simply means and. The semicolon gives a slightly cleaner written connection between two separate but related statements.

Turkish often prefers just putting clauses next to each other without needing ve every time.

Not completely. Turkish word order is flexible, though some orders sound more neutral than others.

The given sentence is natural:

• Termometreyi kullandım; ateşim yüksek değilmiş.

You could also reorder for emphasis, for example:

• Ateşim yüksek değilmiş; termometreyi kullandım.

But that changes the flow. The original order is more natural because it presents:

1. the action of checking
2. the result discovered

So the sentence order matches the logic of the situation.

Because Turkish usually uses the possessive suffix alone unless extra emphasis is needed.

• ateşim = my fever
• benim ateşim = my fever, with stronger emphasis on my

So:

• Ateşim yüksek değilmiş is the normal way
• Benim ateşim yüksek değilmiş could be used if you want contrast, like my fever isn’t high, but yours is

The ğ in Turkish usually is not pronounced like a strong consonant.

In değilmiş, it mainly lengthens or smooths the vowel before it. So it sounds roughly like:

• de-il-miş or dee-il-mish

Not exactly two fully separate syllables in a clunky way, but the ğ is soft and does not sound like English g.

So do not pronounce it like degilmish with a hard g.

It is a borrowed international word, clearly related to English thermometer.

Turkish pronunciation and spelling are adapted to Turkish sound patterns:

• English: thermometer
• Turkish: termometre

Many scientific and technical words in Turkish are recognizable to English speakers in this way.