The word 'swale' originates from Middle English swale, meaning a shady or cool place. It is likely derived from Old Norse svalr, meaning 'cool'. The semantic journey connects the concept of a cool, shaded area to a topographical depression, as such low-lying land is often shaded, damp, and cooler than the surrounding higher ground. This term entered the English lexicon from the language of the Norse settlers and evolved to specifically describe a landscape feature in both agricultural and general topographical contexts.

The word 'swale' is a simplex word of English origin. It is not productively formed from smaller, recognizable morphemes in modern English.