wajib

obligatory; mandatory; compulsory

From Arabic واجب (wājib). Very common in formal and everyday contexts. E.g. wajib pajak (taxpayer, lit. obligated to tax), wajib belajar (compulsory education).

must; have to (informal emphasis)

Used colloquially as an emphatic "must": Kamu wajib coba! (You absolutely must try it!).