In linguistics, sound symbolism is the resemblance between sound and meaning. It is a form of linguistic iconicity. For example, the English word ding may sound similar to the actual sound of a bell. Linguistic sound may be perceived as similar to not only sounds, but also to other sensory properties, such as size, vision, touch, or smell, or abstract domains, such as emotion or value judgment. Such correspondence between linguistic sound and meaning may significantly affect the form of spoken languages.
In Cratylus, Plato has Socrates commenting on the origins and correctness of various names and words. When Hermogenes asks if he can provide another hypothesis on how signs come into being (his own is simply 'convention'), Socrates initially suggests that they fit their referents in virtue of the sounds they are made of:
Now the letter rho, as I was saying, appeared to the imposer of names an excellent instrument for the expression of motion; and he frequently uses the letter for this purpose: for example, in the actual words rein and roe he represents motion by rho; also in the words tromos (trembling), trachus (rugged); and again, in words such as krouein (strike), thrauein (crush), ereikein (bruise), thruptein (break), kermatixein (crumble), rumbein (whirl): of all these sorts of movements he generally finds an expression in the letter R, because, as I imagine, he had observed that the tongue was most agitated and least at rest in the pronunciation of this letter, which he therefore used in order to express motion
However, faced by an overwhelming number of counterexamples given by Hermogenes, Socrates has to admit that "my first notions of original names are truly wild and ridiculous".
The Upanishads and Vyākaraṇa contain a lot of material about sound symbolism, for instance:
The mute consonants represent the earth, the sibilants the sky, the vowels heaven. The mute consonants represent fire, the sibilants air, the vowels the sun... The mute consonants represent the eye, the sibilants the ear, the vowels the mind.