itihāsa

1. history in general.

2. a book which contains instructions on dharma, artha, kāma, and mokṣa, and narrations of ancient events

dharmārtha-kāma-mokṣāṇām

upadeśa-samanvitam |

pūrva-vṛta kathā-yuktam

itihāsaṁ pracakṣate ||

This definition is quoted in Gauḍīya-Vaiṣṇava-abhidhāna.

3. the fifth Veda. According to both śruti and smṛti, the Itihāsa and the Purāṇas are considered the fifth Veda. Śrīmad-Bhāgavatam (3.12.39) states, itihāsa-purāṇāni pañcamaṁ vedam; and (1.4.20), itihāsa purāṇañ ca pañcamo veda ucyate. In his commentary on (1.4.20), Jīva Gosvāmī quotes the Mahābhārata (Mokṣa-dharma 340.21), vedān adhyāpayāmāsa mahābhārata-pañcamān iti, “Vyāsa taught the Vedas along with the fifth of their number, the Mahābhārata.” Similarly in Manu-smṛti (3.232) it is said, ākhyānānītihāsaṁś ca. In his Manu-vartha-muktāvalī commentary on this śloka, Kullūka Bhaṭṭa (a celebrated commentator on Manu-smṛti from the twelfth century) states, itihāsān mahābhāratādīn, “The word itihāsān refers to the Mahābhārata and other literature.” These references establish that the word itihāsa specifically refers to the Mahābhārata. Within the Mahābhārata is found the Bhagavad-gītā, which is accepted as the essence of all the Vedas even by Śrī Śaṅkarācārya, who states in the introduction to his Gītā commentary, tad idaṁ gītā-śāstraṁ samasta-vedārtha-sāra-saṅgraha-bhūtam, “This Gītā-śāstra is the essence of the purport of all the Vedas.” This further confirms that the itihāsa is part of the body of Vedic literature. Śruti itself (Chāndogya Upaniṣad 7.1.2) declares that the Itihāsa and Purāṇas are the fifth Veda among the body of Vedic literature, itihāsaṁ purāṇaṁ pañcamaṁ vedānāṁ vedam.

✍ Smṛti includes the six Vedāṅgas, the dharma-śāstras such as Manu-saṁhitā, the Purāṇas and the itihāsas.

✍ This further confirms that the itihāsa is part of the body of Vedic literature.