The Vedāṅga, which deals with etymological interpretation is called Niruktam; it is considered the ears of the Vedapuruṣa. While Vyākaraṇam deals with the Śabda (form), Niruktam deals with the Artha (meaning). The purpose of the study of this Vedāṅga is Mokṣa. The origin of the thesaurus and dictionary, or Nighaṇṭu, can be traced to Niruktam. The Niruktam was authored by the sage Yāska. The Vedāṅga discusses the four-fold division of the Śabda, the constant change of a thing through six stages etc. Niśśeṣeṇa ucyate arthaḥ anena (the meaning is completely explained by this) — is the derivative meaning of the term Niruktam.
Just like any Vedāṅga, Niruktam can be traced to the Vedas —
तदाहुतीनाम् आहुतित्वम् ॥ ऐतरेयब्राह्मणम् १-१-२॥
tadāhutīnām āhutitvam ॥ aitareyabrāhmaṇam 1-1-2 ॥ tat = that, āhutitvam = oblationness, āhutīnām = of oblations.
This is the oblationness of oblations
यदप्रथयत्, तत् पृथिव्याः पृथिवीत्वम् ॥ तैत्तिरीयब्राह्मणम् १-१-३-६, ७ ॥
yadaprathayat, tat pṛthivyāḥ pṛthivītvam ॥ taittirīyabrāhmaṇam 1-1-3-6, 7 ॥ yat = due to which reason, aprathayat = extended, tat = that is, pṛthivītvam = earthness, pṛthivyāḥ = of the earth.
Due to which reason, it extended; the same is earthness of earth.
Structure of Niruktam
Yāska’s treatise Niruktam is divided into three Kāṇḍas (parts). Each Kāṇḍa is divided into Adhyāyas (chapters). The treatise is also called Samāmnāya (a group of Vedic Śabdas).
- Naighaṇṭukam Kāṇḍam — Nighaṇṭu means thesaurus (a book of synonyms), and refers to the first three chapters. The Naighaṇṭukam Kāṇḍam is the first thesaurus. It was created by Yāska as part of the Niruktam for the the Vedic Śabdas. The authors of Nāmaliṅgānuśāsana — Amarakośa, Vaijayantī, and Halāyudha — followed suit in compiling their thesauruses for Laukika Śabdas (secular words). So, the designation, i.e. Naighaṇṭukam conforms to meaning.
- Naigamam Kāṇḍam — Nigama means Veda. Yāska deals with the Vedic Śabdas in the four chapters (caturadhyāyātmaka) of the second part, called Naigamakāṇḍam.
- Daivatam Kāṇḍam — The third part of Niruktam exclusively deals with Devatas (Gods), the hymns (ṛcaḥ) associated with them, and matters related to the different Devatas. There are five chapters in this part.