Vaisesika Sūtra 2.2.21

श्रोत्रग्रहणोयोऽर्थः स शब्दः ॥२१॥

śrotragrahaṇoyo'rthaḥ sa śabdaḥ ॥21॥

[श्रोत्र (śrotra): Ear or hearing; ग्रहण (grahaṇa): Grasping or understanding; अर्थ (artha): Meaning or object; यः (yaḥ): Which; अर्थः (arthaḥ): Meaning or object; सः (saḥ): That; शब्दः (śabdaḥ): Word;]

The meaning grasped by hearing, that is the sound of the word.