Me: The question is, how would you express that concept in a single word these days now, that irresponsible has taken on a different meaning? (bolded comma added by eta)

Eta: change? (putting an (mis)understood comma where mayhaps it don't belong...)

I think it was Oscar Wilde who, when asked how his latest work was coming along, answered that he'd spent the morning inserting a comma and the afternoon taking it out again.

If I had put in another comma, I would've written the sentence thusly:

The question is, how would you express that concept in a single word these days, now that irresponsible has taken on a different meaning?

Bingley

Bingley