The word Vedānta is a compound, called tatpuruṣa-samāsa of two words Veda and anta (end). This compound word means the end portion (anta) of the Vedas. This word is synonymous with Upaniṣads. Veda is derived from the verb vid (2, P) ‘to know’ with the suffix a, the substantive means ‘knowledge’. Vedānta, that is Upaniṣads, being part of the Vedas, is a pramāṇa, a valid source of knowledge pertaining to matters that cannot be figured out by exercising any other means of knowledge available to mankind – heavens, rituals and the nature of oneself.
Technical: Resolution of Vedānta, a ṣaṣṭītatpuruṣasamāsa(sixth case tatpuruṣa compound) – vedānām antaḥ. Vid + ghañ = ved + a = veda. The code ñ of the suffix ghañ brings about a guṇa change to the vowel e of vid, the corresponding guṇa vowel being e. The initial consonant is not relevant to this derivation.
Anta is formed thus: (verb) am (1 P) + (Uṇādi suffix) tan = am+ta = an + ta = anta, note final consonant of the coded suffix has no impact in the derivation. The m of am changing to n is due to a consonant sandhi rule that mandates change of the preceding m, labial nasal to the nasal of the following letter’s class, here the following letter is a dental, m is thus changed to n.
When a compound is formed, the component words revert to their substantive form to yield the compound which also is a substantive. The declensional suffix is added to the compound to make it a word, depending on the syntactical need in actual usage.