the word 'swash' is an excellent example of onomatopoeia, where the sound of the word imitates the action it describes. it first appeared in english in the mid-16th century, likely coined to mimic the noisy, splashing sound of water dashing against something, like a shore or the side of a boat. this core sense of a striking or splashing sound naturally extended to describe the swaggering, blustering behavior of a person who makes a similarly loud and showy impact. thus, the word's journey is not one of classical roots combining, but rather a direct sensory imitation that broadened into a metaphorical meaning for human conduct.

this word is considered unsegmentable into meaningful morphemes within modern english spelling. it is an imitative or onomatopoeic formation.