Most people learn apa kabar? as the Indonesian equivalent of 'how are you?' and stop there. But kabar is the Arabic word for news. The greeting is literally asking what news you have. Once I noticed that, I started looking at Indonesian differently.

Arabic entered Indonesian through Islam, which arrived in waves along the trade routes from the 13th century onward. By the time Indonesia had a standardised national language in the 20th century, Arabic had been baked into the vocabulary for hundreds of years. Conservative estimates put Arabic-derived words at around 10% of core Indonesian vocabulary. Others put it higher. Either way, it's a substantial chunk, and a lot of it is hiding in words you'd never suspect.

The days of the week are a numbers lesson

This one genuinely surprised me. The Indonesian days of the week from Monday to Friday are Arabic cardinal numbers, slightly worn down from centuries of use.

Senin (Monday) comes from ithnayn, the Arabic word for two. Selasa (Tuesday) is from thalatha, three. Rabu (Wednesday) is from arba'a, four. Kamis (Thursday) is from khamis, five. Jumat (Friday) comes from jumu'ah, meaning gathering, which is why it breaks the number pattern: Friday is the day of communal prayer. Sabtu (Saturday) comes from sabt, the day of rest, same root as Sabbath.

Sunday breaks the sequence entirely. It's minggu, which came from the Portuguese word for Sunday, arriving by a completely different historical route. The Arabic word for Sunday is ahad (one, to complete the sequence), and you do see it occasionally in religious contexts, but minggu won the everyday competition.

So five of seven days of the week are Arabic numbers from two to five, plus Friday. I find it strange that textbooks rarely mention this, because it makes the days immediately memorable once you know it.

Words that feel Indonesian but aren't

Waktu (time) is from Arabic waqt. Zaman (era, period) is from Arabic zaman. Sebab (because, cause) is from Arabic sabab. Kabar we've already met. Ilmu (knowledge, science) comes from Arabic 'ilm. Kitab (book, scripture) is from Arabic kitab.

The useful thing about spotting these is that if you already know any Arabic, Swahili, Malay, or Hausa, you might recognise half this vocabulary. The same words spread along the same trade routes that carried Islam across a broad arc from East Africa to Southeast Asia.

For everyone else, the practical upside is simpler: words ending in certain Arabic-sounding clusters often signal Arabic origin. Akibat (consequence) from Arabic aqibah. Amanat (message, mandate) from Arabic amanah. They have a characteristic texture that you start to feel after a while, which is handy when guessing at unfamiliar vocabulary.

Selamat is doing a lot of work

Selamat deserves its own paragraph. It's everywhere. Selamat pagi (good morning), selamat makan (enjoy your meal), selamat ulang tahun (happy birthday), selamat jalan (safe travels). The word itself comes from Arabic salama, to be safe, the same root as Islam and the Arabic greeting assalamu alaikum.

There's something that gets to me about using the word 'safe' as your all-purpose congratulation. Good morning (be safe in the morning). Happy birthday (be safe on your birthday). It gives selamat a warmth that 'congratulations' in English doesn't quite carry.

The word also shows up shortened to salam in written messages, as a sign-off. Same Arabic root, just a bit less worn down.

The everyday religious layer

Some Arabic words in Indonesian are straightforwardly religious: doa (prayer, supplication), surga (heaven), neraka (hell), malaikat (angel), iman (faith), halal (permitted), haram (forbidden). These came in with Islam and largely stayed in their religious context.

But others have drifted into general use. Rezeki (from Arabic rizq, provision or sustenance from God) now means good fortune, a windfall, a lucky break. You'll hear it used by non-Muslims. Ikhlas (from Arabic ikhlas, sincerity) means doing something without expecting anything in return. These words carry an ethical weight that their origins explain.

Maaf (sorry, forgiveness) is another one. It's from Arabic ma'af, meaning pardon. In Indonesian it's the standard everyday apology, from the minor (maaf, permisi when squeezing past someone in a crowd) to the genuine (maaf ya, aku salah: I'm sorry, I was wrong). Knowing the Arabic origin, rooted in the concept of pardon or absolution, gives the word a slightly more meaningful flavour than a throwaway 'sorry' in English might have.

What this actually helps with

Knowing about the Arabic layer won't help you with Indonesian grammar, and it won't get you through a conversation faster. But it does two useful things.

First, meaning. When you encounter an unfamiliar word with a recognisable Arabic root, you can make a reasonable guess. Hadir (present, in attendance) from Arabic hadira. Syarat (condition, requirement) from Arabic shart. Hak (right, entitlement) from Arabic haqq. None of these are guessable from English, but if you've seen the root anywhere else, they click.

Second, it explains some of the texture of Indonesian. Why does maaf feel slightly weightier than a casual apology? Why does selamat feel genuinely warm? Why do Indonesians often say insyaAllah as a real qualifier rather than a dismissal? The Arabic layer is part of why Indonesian has the character it has, and understanding where it came from makes the language feel less arbitrary.

If you want to build this vocabulary properly rather than through lists, the Bahasa.fun course works through words like these in context, which tends to stick better. There's a free tier worth trying first.

For more on where Indonesian vocabulary comes from, the Dutch loanwords post covers the colonial layer, and the English loanwords post covers the more recent wave. Between the three, you start to see why Indonesian vocabulary feels unusually eclectic for a language that looks, on the surface, fairly simple. If you want to practise recognising these words in real sentences, sign up and try the reading exercises.