Ahşap macunu kıymığın bıraktığı deliği doldurdu.

A fairly literal gloss is:

• Ahşap macunu = wood putty / wood filler
• kıymığın = of the splinter / the splinter’s
• bıraktığı = that it left
• deliği = the hole (as the direct object)
• doldurdu = filled

So the structure is roughly:

Wood putty [the splinter-left hole] filled.

Natural English rearranges that as The wood filler filled the hole that the splinter left.

Because ahşap macunu is a noun compound, not a plain noun plus case ending.

In Turkish, compounds like this often work as:

• ahşap = wood
• macun-u = putty + compound ending

So ahşap macunu means wood putty / wood filler.

That -u is not the accusative here. It is the usual compound marker on the second noun. Compare similar patterns such as:

• elma suyu = apple juice
• tahta kapısı = wooden door / door of wood

So even though macunu ends in -u, the whole phrase is still the subject.

Doldurdu comes from doldurmak, meaning to fill.

Breakdown:

• doldur- = fill
• -du = past tense
• third-person singular has no extra ending here

So doldurdu means he/she/it filled or simply filled.

In this sentence, the understood subject is ahşap macunu, so the meaning is the wood putty filled.

Because it is the subject of a -DIK relative clause.

In Turkish, when you make a clause like that the splinter left, the subject of that clause usually goes into the genitive:

• kıymık = splinter
• kıymığın = the splinter’s / of the splinter

So:

• kıymığın bıraktığı = that the splinter left

This is very common in Turkish:

• benim gördüğüm ev = the house that I saw
• adamın yaptığı yemek = the food that the man made

It is a relative/participle form of bırakmak (to leave).

Very roughly:

• bırak- = leave
• -DIK = relative-clause/participle suffix
• -I = agreement suffix matching the genitive subject

So:

• kıymığın bıraktığı = that the splinter left

A useful comparison:

• benim yazdığım mektup = the letter that I wrote
• onun aldığı kitap = the book that he/she bought

Here, bıraktığı is doing the same job: it turns a whole clause into something that can describe a noun.

Because the noun being described, delik (hole), is not the subject of bırakmak. It is the thing affected by the action.

In Turkish:

• -An is typically used when the described noun is the subject of the verb.
• -DIK is typically used when the described noun is not the subject, often the object.

So:

• bırakan kıymık = the splinter that left ...
  Here the described noun is kıymık, the doer.

But in your sentence:

• kıymığın bıraktığı delik = the hole that the splinter left
  Here the described noun is delik, not the doer.

That is why -DIK is the right pattern.

Because it is the definite direct object of the main verb doldurdu.

Turkish often marks a specific direct object with the accusative ending:

• delik = hole
• deliği = the hole / the hole as a specific object

In this sentence, the hole is clearly specific because it is identified by the relative clause:

• kıymığın bıraktığı delik = the hole that the splinter left

Since that is a definite, identifiable hole, accusative marking is natural:

• kıymığın bıraktığı deliği doldurdu = filled the hole that the splinter left

This is because of normal Turkish sound changes when suffixes are added.

Two important things are happening:

1. Vowel harmony changes the vowel in the suffix.

   • -ın / -in / -un / -ün
   • -ı / -i / -u / -ü

2. Final k often softens to ğ before a vowel-initial suffix.

   • kıymık + ın → kıymığın
   • delik + i → deliği

You also see something similar in bıraktığı:

• bırak + dık + ı → bıraktığı

So these shapes may look different at first, but they are regular and very common in Turkish.

Because Turkish puts modifiers before the noun they modify.

English says:

• the hole that the splinter left

Turkish says, more literally:

• the splinter-left hole
• kıymığın bıraktığı delik

This is normal Turkish word order for relative clauses. The whole descriptive part comes before the noun.

The sentence follows a very typical Turkish pattern:

• Subject: Ahşap macunu
• Object: kıymığın bıraktığı deliği
• Verb: doldurdu

So it is basically subject–object–verb.

That is one reason the verb comes at the end. Turkish often saves the main verb for last.

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

Instead, Turkish shows definiteness and specificity in other ways, such as:

• context
• word order
• accusative marking on direct objects

So in this sentence:

• deliği is understood as a specific hole partly because it has the accusative ending
• ahşap macunu is understood from context as the wood putty or simply wood filler

English needs articles; Turkish usually does not.