Learn Hardcore Indonesian: Gawai itu milik adik perempuan saya. - That gadget belongs to my younger sister.

Gawai means device / gadget, usually an electronic one. In practice, it often refers to things like smartphones, tablets, or other digital gadgets.

Usage notes:

Many people still say HP (from “handphone”) or telepon / telefon for phone.
Gawai is a bit more formal and is common in the media, education, and official contexts, but you will also hear it in daily conversation, especially among people who like more standard Indonesian.
It’s broader than just “phone”: a gawai could be a phone, a tablet, a smart watch, etc., depending on context.

So in this sentence, gawai is best understood as the gadget / the device.

Why does itu come after gawai, not before it, and what nuance does it add?

In Indonesian, demonstratives like ini (this) and itu (that) usually come after the noun:

gawai itu = that device / the device
gawai ini = this device

Functions of itu here:

It can mean “that” (a device that’s not near the speaker, or mentioned before), or
It can act like “the” in English, just marking the noun as specific/known.

You generally do not say itu gawai to mean “that device”. Itu gawai would sound like “that (is a) device” or start a different kind of sentence.

So gawai itu = “that device” / “the device (we’re talking about)”.

What is milik here? Is it a verb like “to own” or “to belong to”?

Milik is related to the idea of ownership / possession. In this pattern:

X milik Y ≈ X belongs to Y / X is Y’s

So:

Gawai itu milik adik perempuan saya.
= That device belongs to my younger sister.
= That device is my younger sister’s.

Some points:

Grammatically, milik is often treated like a noun (“ownership”), but in sentences like this it behaves almost like a preposition or linking word: [thing] milik [owner].
It is not used like a normal verb with prefixes. For example,
- ✅ Gawai itu milik saya.
- ❌ Gawai itu memiliki saya. (“The device owns me” – wrong meaning here.)

So you can remember the pattern as: Thing + milik + owner.

How is milik different from punya? Could I say Gawai itu punya adik perempuan saya?

Yes, you can say:

Gawai itu punya adik perempuan saya.

This is very natural and common in everyday speech and means the same thing:

That device is my younger sister’s / belongs to my younger sister.

Differences:

milik
- More formal, neutral, used in written language, news, official contexts.
- Slightly more detached or objective in tone.
punya
- More colloquial / everyday.
- Very common in spoken Indonesian among friends and family.

In speech, punya is probably more common; in writing or formal explanations, milik is very normal.

Can I add adalah in the sentence: Gawai itu adalah milik adik perempuan saya? Is that better or worse?

You can say:

Gawai itu adalah milik adik perempuan saya.

This is grammatically correct and sounds a bit more formal or textbook-like.

Comparison:

Gawai itu milik adik perempuan saya.
- Natural, simple, and very common.
Gawai itu adalah milik adik perempuan saya.
- Also correct, more formal / explanatory, often seen in written Indonesian, schoolbooks, or careful speech.

Adalah works like a copula (“is”) linking subject and predicate, but it’s optional here. You do not need it for the sentence to be correct.

What exactly does adik perempuan mean? Is it just “sister” or specifically “younger sister”?

Adik means younger sibling, without specifying gender.
Perempuan means female / woman.

So adik perempuan together means younger sister.

Some related words:

adik = younger sibling (gender not specified)
adik perempuan = younger sister
adik laki-laki = younger brother
kakak = older sibling (gender not specified)
kakak perempuan = older sister
kakak laki-laki / abang (in some regions) = older brother

In your sentence:

adik perempuan saya = my younger sister

Why is it adik perempuan saya and not saya adik perempuan? How does possession word order work?

In Indonesian, the possessor usually comes after the thing possessed. The basic pattern is:

[thing] [possessor]

Here:

adik perempuan = younger sister
saya = I / me
adik perempuan saya = my younger sister (“younger sister of me”)

So:

adik perempuan saya = my younger sister
gawai saya = my device
rumah mereka = their house

Saya adik perempuan would mean something like “I (am) the younger sister” in the right context, not “my younger sister”.

Could this sentence be talking about more than one device, like “Those devices are my younger sister’s”?

By itself, Gawai itu milik adik perempuan saya is most naturally understood as singular:

gawai (no reduplication, no number word) = a device / the device
itu = that / the

Indonesian usually does not mark plural on nouns, but context and extra words show plurality. To clearly indicate plural, you might say:

Gawai-gawai itu milik adik perempuan saya.
(“Those devices are my younger sister’s.”)
Semua gawai itu milik adik perempuan saya.
(“All those devices are my younger sister’s.”)

Without those, the default reading is “That device is my younger sister’s.”

If I want to say “That device is my younger brother’s” instead, what should I change?

You only need to change perempuan (female) to laki-laki (male):

Gawai itu milik adik laki-laki saya.
= That device belongs to my younger brother.

Summary of the patterns:

adik perempuan saya = my younger sister
adik laki-laki saya = my younger brother

How does saya compare with aku here? Could I say adik perempuan aku or use -ku?

Saya and aku both mean I / me, but:

saya = more formal / neutral / polite, safe in most situations
aku = more informal / intimate, used with friends, family, etc.

Possible possessive forms:

adik perempuan saya
adik perempuan aku (informal)
adik perempuanku (using the suffix -ku, which means “my”)

All three can mean “my younger sister”. The difference is mainly formality and style:

In neutral or formal Indonesian, adik perempuan saya is the safest choice.
In casual conversation or writing between close people, adik perempuanku or adik perempuan aku is common.

In your original sentence, saya matches the slightly more neutral/formal tone of milik.