n. The strongest version of an opponent’s argument, particularly when this version improves upon the opponent’s original argument.
2012
You know when someone makes an argument, and you know you can get away with making it seem like they made a much worse one, so you attack that argument for points? That’s strawmanning. Lots of us have done it, even though we shouldn’t. But what if we went one step beyond just not doing that? What if we went one better? Then we would be steelmanning, the art of addressing the best form of the other person’s argument, even if it’s not the one they presented.
2011
Sometimes the term "steel man" is used to refer to a position's or argument's improved form. A straw man is a misrepresentation of someone's position or argument that is easy to defeat: a "steel man" is an improvement of someone's position or argument that is harder to defeat than their originally stated position or argument.
2003 (earliest)
You know, this straw man is so big and so strong that he'll soon morph into a steel man.
According to the OED, the earliest use of straw man dates to 1896, when the political theorist Leonard Trelawny (L. T.) Hobhouse, in his book Theory of Knowledge, wrote "The straw man was easily enough knocked over by the critic who set him up."