Definitional Retreat
Changing the meaning of a word to deal with an objection raised against the original wording.
Origin
British philosopher Madsen Pirie, co-founder of the Adam Smith Institute, named and catalogued this tactic in his 1985 book The Book of the Fallacy, later revised as How to Win Every Argument (2006). The maneuver itself — covertly shifting a word's meaning to dodge a counterargument — is an ancient form of equivocation recognized since Aristotle, but Pirie gave this specific variant its own name and treatment.
Everyday Use
Someone claims "all politicians are corrupt," and when you name an honest one, they respond: "Well, I meant corrupt in the sense of being part of a broken system." They've quietly shifted what "corrupt" means rather than admitting the original claim was too broad. It's a rhetorical escape hatch — change the definition and the objection evaporates.