Other forms: softened, softening, softens
To soften is to make something softer or gentler. Soften the butter, soften the blow, softened his tone.
In cooking it is a precise instruction: soften the onions means cook them until translucent without colouring. Soften the blow means to make bad news easier to take. A position or a tone softens when it becomes less hard, which in politics is reported as a concession. Note softener, as in fabric softener and water softener; and soften up, which means to weaken resistance before asking.
1verbsoftenTo make something softer.
“Leave the butter out of the fridge to soften before you make the cake.”
2verbgentlerTo make something gentler or less severe.
“She softened her voice when she saw how frightened the child was.”
soften is a making softer.
Soft plus -en, the ending that makes verbs meaning to make more so. Harden, sharpen, deepen and weaken are built the same way, and English stopped making new ones several centuries ago.
Middle English
softenen
English, today
soften
From Middle English softenen, softnen, equivalent to soft + en.
Etymology from Wiktionary, CC BY-SA