Standard Hindi derives much of its formal and technical vocabulary from Sanskrit. Standard or shuddh ("pure") Hindi is used only in public addresses and radio or TV news, while the everyday spoken language in most areas is one of several varieties of Hindustani, whose vocabulary contains words drawn from Persian and Arabic. In addition, spoken Hindi includes words from English and other languages as well.

Vernacular Urdu and Hindi share the same grammar and core vocabulary and so are practically indistinguishable. However, the literary registers differ substantially in borrowed vocabulary; in highly formal situations, the languages are barely intelligible to speakers of the other. Hindi has looked to Sanskrit for borrowings from at least the 19th century, and Urdu has looked to Persian and Arabic for borrowings from the eighteenth century. On another dimension, Hindi has been associated with the Hindu community and Urdu with the Muslim community.

There are five principal categories of words in Standard Hindi:

Tatsam (तत्सम्) words: These are the words which have been directly borrowed from Sanskrit to enrich the formal and technical vocabulary of Hindi. Such words (mostly nouns and adjectives) have been borrowed without any orthographic adaptation. Pronunciation, however, conforms to Hindi norms. Among nouns, the tatsam word could be the Sanskrit uninflected word-stem, or it could be the nominative singular form in the Sanskrit nominal declension.

Ardhatatsam words: These are words that were borrowed from Sanskrit in the middle Indo-Aryan or early New Indo-Aryan stages. Such words typically have undergone sound changes subsequent to being borrowed.

Tadbhav (तद्भव) words: These are inherited words from Sanskrit. They have undergone all of the sound changes affecting the stages of Indo-Aryan between Sanskrit and Hindi.

Deshaj (देशज) words: These are words that were not borrowings but do not derive from attested Indo-Aryan words either. Belonging to this category are onamatopoetic words.

Videshi words: these include all words borrowed from sources other than Indo-Aryan. The most frequent sources of borrowing in this category have been Persian, Arabic, and English.

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Similarly, Urdu treats its own vocabulary, borrowed directly from Persian and Arabic, as a separate category for morphological purposes.

Hindi from which most of the Persian, Arabic and English words have been ousted and replaced by tatsam words is called Shuddha Hindi (pure Hindi). Chiefly, the proponents of the so-called Hindutva ("Hindu-ness") are vociferous supporters of Shuddha Hindi.

Excessive use of tatsam words sometimes creates problems for most native speakers. Strictly speaking, the tatsam words are words of Sanskrit and not of Hindi—thus they have complicated consonantal clusters which are not linguistically valid in Hindi. The educated middle class population of India can pronounce these words with ease, but people of rural backgrounds have much difficulty in pronouncing them. Similarly, vocabulary borrowed from Persian and Arabic also brings in its own consonantal clusters and "foreign" sounds, which may again cause difficulty in speaking them.