Bouba/kiki effect
The bouba–kiki effect ( BOO-bə KEE-kee) or takete–maluma phenomenon is a non-arbitrary mental association between certain speech sounds and certain visual shapes. The most typical research finding is that people, when presented with nonsense words, tend to associate certain "soft" sounds (like bouba and maluma) with a rounded shape and other "hard" sounds (like kiki and takete) with a spiky shape.