The word 'swap' emerged in Middle English, first appearing around the 13th century as 'swappen,' meaning to strike or hit. This sense is believed to be onomatopoeic, imitating the sound of a blow. By the 16th century, the meaning had evolved from the physical act of striking hands together in a bargain to the more abstract and peaceful concept of exchanging one thing for another. This semantic shift from a forceful action to a mutual trade illustrates how commercial and social interactions can soften the connotations of originally vigorous terms.

This is a simplex word of imitative origin, likely representing the sound of a slap or a quick, sharp movement associated with an exchange or strike. Its functional role is as a whole word.