Saya menulis arti kata baru dan sinonimnya di buku catatan.

Yes. Saya means I and is the standard, polite way to say it in Indonesian.

• Saya = I
• It is more neutral/formal than aku
• In everyday speech, Indonesians may sometimes drop the subject if it is already clear from context, but keeping Saya makes the sentence complete and clear

So Saya menulis ... means I write / I am writing / I wrote ..., depending on context.

Tulis is the root word, meaning write.
Menulis is the active verb form built from that root.

• root: tulis
• active verb: menulis = to write

This is very common in Indonesian. Many verbs use the meN- prefix to form an active verb.

So:

• tulis = write, writing, the idea of writing
• menulis = to write / write actively

In a normal sentence with a subject doing the action, menulis is the expected form.

It can mean any of those, depending on context. Indonesian verbs do not change form for tense the way English verbs do.

So Saya menulis ... could mean:

• I write ...
• I am writing ...
• I wrote ...

If the speaker wants to make time clearer, they can add words like:

• sedang = currently / in the middle of
• tadi = earlier
• kemarin = yesterday
• besok = tomorrow

Without a time word, the tense is understood from context.

Arti means meaning.

So:

• arti kata = the meaning of a word

In this sentence, arti kata baru means the meaning of the new word.

A closely related word is makna, which also means meaning, but arti is very common and natural here.

Here it means new word.

In Indonesian, adjectives usually come after the noun:

• kata baru = new word
• literally: word new

If you wanted to talk about the word baru itself, you would usually make that clearer, for example:

• kata “baru”
• or kata baru itu, depending on context

So in this sentence, kata baru is best understood as a new word that the speaker has learned.

The ending -nya often means its, his/her, or sometimes the, depending on context.

So sinonimnya here means something like:

• its synonym
• its synonyms
• or more naturally in English, the word’s synonym(s)

In this sentence, -nya refers back to kata baru.

So:

• sinonimnya = its synonym(s), meaning the synonym(s) of the new word

This makes the connection clear: the speaker writes down both the meaning of the new word and its synonym(s).

It can be either, depending on context.

Indonesian nouns usually do not have a special form for singular vs. plural the way English does. So:

• sinonim can mean synonym or synonyms
• sinonimnya can mean its synonym or its synonyms

In real usage, context tells you which one is meant. In a sentence like this, English often translates it naturally as its synonym(s).

If a speaker really wants to show plurality clearly, they might use reduplication:

• sinonim-sinonimnya = its synonyms

But the shorter sinonimnya is very normal.

Dan means and.

Here it connects two things that the speaker writes down:

• arti kata baru = the meaning of the new word
• sinonimnya = its synonym(s)

So the structure is:

• Saya menulis
  • arti kata baru
    • dan
      • sinonimnya
        • di buku catatan

In other words, the speaker writes down both the meaning and the synonym(s).

Because this di is a preposition, meaning in, at, or on.

• di buku catatan = in the notebook

When di is a preposition showing location, it is written separately from the following word.

Compare that with the prefix di- used in passive verbs, which is written together:

• ditulis = written / is written

So:

• di buku catatan = correct, because di means in
• dibuku catatan = incorrect in this sentence

This is a very common thing for learners to notice.

Buku catatan means notebook.

Literally:

• buku = book
• catatan = notes / note-taking record

Together, buku catatan means notebook or exercise book / note book, depending on context.

Indonesian often uses noun + noun combinations like this instead of making one single word. So even though English has the one-word form notebook, Indonesian naturally says buku catatan.

That is a very normal word order in Indonesian.

The sentence is structured like this:

• Saya = subject
• menulis = verb
• arti kata baru dan sinonimnya = object
• di buku catatan = place/location

Putting the location at the end is natural and common, much like in English:

• I write the meaning of the new word and its synonym(s) in my notebook.

Indonesian word order is often flexible, but this version sounds straightforward and standard.

Yes, menuliskan is also possible in many contexts, but it gives a slightly different nuance.

• menulis = to write
• menuliskan = to write something down / to write something for someone or onto something, often with a bit more focus on the thing being written

So:

• Saya menulis arti kata baru dan sinonimnya di buku catatan.
  = very natural, simple, and correct

A version with menuliskan could also work, especially if you want to emphasize writing those items down. But menulis is perfectly normal here.

You can sometimes omit it if the subject is already obvious from context.

For example, in a conversation, someone might simply say:

• Menulis arti kata baru dan sinonimnya di buku catatan.

But as a full standalone sentence, Saya menulis ... is clearer and more complete.

So:

• with Saya = clear, explicit, standard
• without Saya = possible in context, but less complete on its own

For learners, keeping Saya is usually the safest choice.