As far as I (as non-native speaker) understand the words as in, this is short for for instance, as in:
It's my impression that at some point in time people started to use as in in an ironical way, like:
He's dead, as in not alive.
Is this impression correct or have the words as in always been used this way? If this ironic use developed later, when was that?
Best Answer
"As in" has always been used to provide a concrete example of a word. I would say that it has always had a slightly sarcastic or incredulous tone to it - it could be used to describe, say, a piece of art "its made of carrier bags - as in what you take your shopping home in".
The use more recently as in the OP is just taking this one stage further - using an accepted linguistic trick to make a point. "Dead - as in no longer alive" can be used to emphasise the point to someone - along the lines of "when I say dead, I mean dead. Not injured, dead. No longer alive, never coming back". I have heard it used not ironically, but more in this form for emphasis, to make sure the person has understood, when they may be struggling to understand.