[citation needed] Besides some grammatical simplification, Tetun Dili has been greatly influenced by the vocabulary and to a small extent by the grammar of Portuguese, the other official language of East Timor.

[5] Although this coincides with the favoured Indonesian form, and the variant with m has a longer history in English, Tetun has also been used by some Portuguese-educated Timorese, such as José Ramos-Horta and Carlos Filipe Ximenes Belo.

The Portuguese (present in Timor from c. 1556) made most of their settlements in the west, where Dawan was spoken, and it was not until 1769, when the capital was moved from Lifau (Oecussi) to Dili that they began to promote Tetum as an inter-regional language in their colony.

[13] After the United Nations Transitional Administration in East Timor (UNTAET) took over governance in 1999, Tetun (Dili) was proclaimed the country's official language, even though according to Encarta Winkler Prins it was only spoken by about 8% of the native population at the time, while the elite (consisting of 20 to 30 families) spoke Portuguese and most adolescents had been educated in Indonesian.

[15] In addition to regional varieties of Tetum in East Timor, there are variations in vocabulary and pronunciation, partly due to Portuguese and Indonesian influence.

The Tetum spoken by East Timorese migrants living in Portugal and Australia are more Portuguese-influenced, as many of those speakers were not educated in Indonesian.

Tetum has an optional indefinite article ida ('one'), used after nouns: There is no definite article, but the demonstratives ida-ne'e ('this one') and ida-ne'ebá ('that one') may be used to express definiteness: In the plural, sira-ne'e ('these') or sira-ne'ebá ('those') are used: The particle nia forms the inalienable possessive, and can be used in a similar way to 's in English, e.g.: When the possessor is postposed, representing alienable possession, nia becomes nian: Like other Austronesian languages, Tetum has two forms of we, ami (equivalent to Malay kami) which is exclusive, e.g. "I and they", and ita (equivalent to Malay kita), which is inclusive, e.g. "you, I, and they".

To form adjectives and actor nouns from verbs, the suffix -dór (derived from Portuguese) can be added: Tetum does not have separate masculine and feminine gender, hence nia (similar to ia/dia/nya in Malay) can mean either 'he', 'she' or 'it'.

In some instances, the different gender forms have distinct translations into English: In indigenous Tetum words, the suffixes -mane ('male') and -feto ('female') are sometimes used to differentiate between the genders: Superlatives can be formed from adjectives by reduplication: When making comparisons, the word liu ('more') is used after the adjective, optionally followed by duké ('than' from Portuguese do que): To describe something as the most or least, the word hotu ('all') is added: Adverbs can be formed from adjectives or nouns by reduplication: The most commonly used prepositions in Tetum are the verbs iha ('have', 'possess', 'specific locative') and baa/ba ('go', 'to', 'for').

For example, the verb haree ('see') in Tetun-Terik would be conjugated as follows: Whenever possible, the past tense is simply inferred from the context, for example: However, it can be expressed by placing the adverb ona ('already') at the end of a sentence.

'[16] As Tetum did not have any official recognition or support under either Portuguese or Indonesian rule, it is only recently that a standardised orthography has been established by the National Institute of Linguistics [tet; pt] (INL).

The current orthography originates from the spelling reforms undertaken by Fretilin in 1974, when it launched literacy campaigns across East Timor, and also from the system used by the Catholic Church when it adopted Tetum as its liturgical language during the Indonesian occupation.

These involved the transcription of many Portuguese words that were formerly written in their original spelling, for example, educação → edukasaun 'education', and colonialismo → kolonializmu 'colonialism'.

Reforms suggested by the International Committee for the Development of East Timorese Languages (IACDETL) in 1996 included the replacement of the digraphs ⟨nh⟩ and ⟨lh⟩ (borrowed from Portuguese, where they stand for the phonemes /ɲ/ and /ʎ/) with ⟨n̄⟩ and ⟨l̄⟩ , respectively (as in certain Basque orthographies), to avoid confusion with the consonant clusters /nh/ and /lh/, which also occur in Tetum.

Some linguists favoured using ⟨ny⟩ (as in Catalan and Filipino) and ⟨ly⟩ for these sounds, but the latter spellings were rejected for being similar to the Indonesian system, and most speakers actually pronounce ñ and ll as [i̯n] and [i̯l], respectively, with a semivowel [i̯] which forms a diphthong with the preceding vowel (but reduced to [n], [l] after /i/), not as the palatal consonants of Portuguese and Spanish.

In the sociolect of Tetum that is still used by the generation educated during the Indonesian occupation, [z] and [ʒ] may occur in free variation.