The word 'welter' has a robustly physical origin, entering English from the Germanic languages of the Low Countries, where it described the literal, tumultuous motion of rolling or wallowing, as in mud or water. This core sense of chaotic, uncontrolled movement traveled with the word into English, where it first applied to the violent, tumbling action of waves or a person thrashing about. Over time, the logic of this physical turbulence was extended metaphorically, allowing 'welter' to describe any overwhelming, disordered mass or state of confusion, such as a welter of details or a welter of emotions, thus evolving from a concrete action to an abstract condition.

This word is a simplex form. It originates from Middle Dutch or Middle Low German welteren, meaning 'to roll' or 'to wallow'.