the.com/softener

means A substance added during washing or manufacturing that coats or alters fibers to make fabric feel smoother, less static, and more pliable.

from Straightforward agent noun: 'soften' (from Old English 'softe,' meaning gentle or easeful) plus the workaday '-er' that turns any verb into 'the thing that does it.' The word itself has no secret history — it's as plain as its job — but its commercial sense bloomed in the 20th century when chemists began selling bottled gentleness, first for textiles and laundry, later adapted for skin and water, each time promising to undo a little of life's roughness.