How does sound symbolism connect certain speech sounds with shapes or sizes?

Sound symbolism refers to the phenomenon where certain speech sounds appear to have an inherent connection to visual or tactile shapes, rather than being purely arbitrary. While most vocabulary in language is arbitrary, some sound types evoke specific physical qualities through direct association.1

For example, many people intuitively agree that a made-up word like oomboolu is better suited to describe a round, bulbous object than a spiky one. Similarly, the use of high-front vowel sounds—such as the ee in the English word wee or the i in the Italian piccolo—has been traced across several languages as a consistent way to express smallness or diminutive size.1

These instances of sound symbolism represent a small portion of a language's vocabulary, as the vast majority of words lack a direct link between their sound and their meaning.1