Bihari Hindi is a variety of Hindustani, spoken in Bihar, particularly in the urban areas of Bihar. It is heavily influenced by the Bihari languages Magahi, Maithili and Bhojpuri.

Hindi natively possesses a symmetrical ten-vowel system. Instead of [ɛː] and [ɔː], Bihari Hindi has diphthongs [əi/əe] and [əu/əo]. The vowels [ə], [ɪ], [ʊ] are always short in length, while the vowels [ɑː], [iː], [uː], [eː], [oː] are always considered long.

Hindi has four classes of stops, one class of affricate, which is generally treated as a stop series, related nasals, fricatives and approximant.

Standard Hindi distinguishes two genders (masculine and feminine), two noun types (count and non-count), two numbers (singular and plural), and three cases (direct, oblique, and vocative). But in Bihari Hindi, the direct case is most commonly used. Other cases are dormant. The inflectional plural is also not used, the periphrastic plural is used. However, a weak inflected plural is used in Bihari Hindi, borrowed from eastern Hindi and Bhojpuri (-an), though it is declined here only for animates. Nouns are divided into two classes- marked and unmarked, which have no differences except that the marked form is used for declinable adjectives. There is a peculiar long form in Bihari Hindi, for most tadbhava and marked nouns, a feature also prevalent in Maithili, Magahi and Bhojpuri. This form denotes several meanings-

1. It denotes diminutive or often low honour meaning.
2. It also denotes definite nature of the noun.
3. For proper nouns, apart from the diminutive meaning, it also signifies familiarity, especially for personal names.

Weak plurals can also be formed from these long form of the nouns.

Gender system is usually the same as Standard Hindi, but differs in that only animates and real gender is marked in Bihari Hindi, all unmarked inanimates are treated masculine. Therefore, the gender system can be defined as- masculine-neuter and feminine.

The table below displays the suffix paradigms. -Ø denotes that no suffix is added to the noun stem.

Plural is not mandatory, it can be dropped when inanimate or indefinite. The next table of noun declensions, shows the above suffix paradigms in action. Words: laṛkā ('boy'), kū̃ā ('well'), seb ('apple'), balid ('father'), cākū (chūrī is more common, but cākū is a more apt example) ('penknife'), admī ('man'), mitr ('friend'), laṛkī ('girl'), ciṛiyā ('finch'), kitāb ('book'), bhāsā ('language'), and aurat ('woman').

Sometimes, weak plural is also combined with plural marker sab, such as laṛkan sab, laṛkiyan sab, and so on. Also long form can also be combined with plural marker sab, such as laṛkavā sab, laṛkiyā sab.

Notes for noun declension:

• ^1 A small number of marked masculines like kuā̃ display nasalization of all terminations.^[6]
• ^2 Some masculines ending in ā fall in the unmarked category. i.e. bālid (valid in Stabdard Hindi) "father", cacā (cācā in Standard Hindi) "uncle", rājā "king".^[7]
• ^3 Unmarked nouns ending in ū and ī generally shorten this to u and i before the plural termination(s), with the latter also inserting the semivowel y.^[7][8][9]
• ^4 Many feminine Sanskrit loanwords such as bhāsā (bhāṣā in tatsama form) ('language') and mātā (mother) end in ā, therefore the ā is not a reliable indicator of noun gender.^[7]
• The iyā ending is also not a reliable indicator of gender or noun type. Some words such as pahiyā ('wheel') and Persian takiā ('pillow') are masculine marked: pahiyan ('wheels'), takiyan ('pillows'). Feminine loanwords such as Arabic duniā ('world') and Sanskrit kiriyā (krīyā in tatsama form) ('action') use feminine unmarked.
• Perso-Arabic loans ending in final unpronounced h are handled as masculine marked nouns.^[10] Hence bacca(h) → baccā.

Adjectives may be divided into declinable, and indeclinable categories.^[11][12] Declinables of Standard Hindi are marked, through termination, for the gender of the nouns they qualify, and in Bihari Hindi, indeclinable adjectives are also declined, for forming long forms, thus they can be properly said unmarked. Instead of number, adjectives are qualified for honour, a characteristic feature of Bihari languages. For forming long forms, suffix -kā and -kī is used for masculine-neuter and feminine respectively.

Plurals can be made of weak plurals, but not as an adjective. They are rather used as adverbs.

The set of declinable adjective terminations is similar but greatly simplified in comparison to that of noun terminations —

Indeclinable adjectives are completely invariable, and can end in either consonants or vowels (including ā and ī ). A number of declinables display nasalisation of all terminations.^[11]

• Examples of marked (type-1) adjectives: baṛā "big", choṭā "small", moṭā "fat", acchā "good", burā "bad", kālā "black", ṭhaṇḍā "cold".
• Examples of marked (type-2) adjectives: baṛhiyā "great/awesome", ghatiyā "of bad quality or nature", cūtiyā "idiot"/ "asshole".
• Examples of marked (type-3) adjectives: dāyā̃ "right (direction)", bāyā̃ "left (direction)"
• Examples of unmarked adjectives: kharāb "bad", sāph "clean", bhārī "heavy", murdā "dead", sundar "beautiful", pāgal "crazy/mad", lāl "red".

• Schmidt, Hans (2003), "Temathesis in Rotuman" (PDF), in John Lynch (ed.), Issues in Austronesian Historical Phonology, Pacific Linguistics Research School of Pacific and Asian Studies, pp. 175–207, ISBN 978-0-85883-503-0
• Shapiro, Michael C. (2003). "Hindi". In Cardona, George; Jain, Dhanesh (eds.). The Indo-Aryan Languages. Routledge. pp. 250–285. ISBN 978-0-415-77294-5.
• Snell, Rupert; Weightman, Simon (1989). Teach Yourself Hindi (2003 ed.). McGraw-Hill. ISBN 978-0-07-142012-9.