The word 'swishy' is a relatively modern English formation built upon the imitative core 'swish,' which first appeared in the 18th century to directly mimic the sound of a light, rapid movement through air, such as a cane or a skirt. The addition of the productive adjectival suffix '-y,' with its ancient Germanic lineage, transforms this sound into a descriptive property. Thus, the literal "characterized by a swishing sound" seamlessly extends to describe objects, like fabrics or hair, that both produce such a sound and exhibit the loose, flowing motion inherent to creating it. This evolution from an auditory imitation to a multi-sensory descriptive term exemplifies the flexibility of English word formation.

Structure: swish (sound/motion) + y (adjective-forming suffix) - swish: An imitative or onomatopoeic formation from English, representing the sound of something moving quickly through air or liquid. Its functional role is the core semantic root. - y: A native English suffix (from Old English -ig, Proto-Germanic -igaz) used to form adjectives meaning "characterized by; full of; having the quality of."