The word 'swim' originates from the Old English verb 'swimman', meaning "to move in or on the water, float". This Old English term is derived from the Proto-Germanic root 'swemjan-', which carried a sense of "to be in motion". This root can be traced further back to the Proto-Indo-European (PIE) root 'swem(bh)-', meaning "to be unsteady, move, swim". The modern form 'swimming' illustrates a standard English morphological process where the suffix '-ing' is appended to a verb to create a noun denoting the action or activity itself. Thus, the literal sense of "moving in water" has remained remarkably consistent from its ancient PIE ancestor to its current usage.

The word 'swimming' is a modern English gerund and present participle formed by adding the suffix '-ing' to the verb 'swim'. The core verb 'swim' is a simplex word of Old English origin.