Our political vocabulary is changing all the time. Words that loom large in one generation’s national public discourse can almost totally disappear in the next.

Take the word “segregation.”

A half-century ago, newspapers headlined “segregation” on almost a daily basis. This same word seldom appears today, in print or online. To our contemporary sensibilities, segregation seems so, well, yesterday.

But segregation still stains America, and not just the lingering legacy of the racial segregation that Americans battled decades ago. America now faces stark income segregation as well — and this income segregation is getting worse.

Census Bureau researchers have just released a new report that details one aspect of this new segregation: the concentration of high-income households by metro area.

How concentrated have high-income households become? In some metro areas, the new Census data show, you can knock randomly on 100 doors and expect to find only one household making at least $191,469, the income threshold for entering America’s top 5 percent between 2006 and 2011.

In other metro areas, that same door-knocking would turn up as many as 18 households making near $200,000 and above.

Our contemporary income segregation becomes even more intense when we drill down from the metro to neighborhood level. Back in 1970, sociologists Sean Reardon and Kendra Bischoff have detailed, 65 percent of America’s families lived in “middle-income” situations, neighborhoods where incomes range from 80 to 125 percent of the median — the most typical — income of the larger metro area.

By 2008, only 43 percent of U.S. families lived in middle-income neighborhoods.

Meanwhile, over that same span, the share of families living in distinctly poor and distinctly rich neighborhoods doubled.

In 2008, nearly one in three metro-area U.S. families lived at these extremes, either in poor neighborhoods with incomes under 67 percent of the metro median, or in affluent neighborhoods with incomes above 150 percent of that level.

Today’s affluent Americans, add sociologists Reardon and Bischoff, actually live more segregated lives than the poor. They’ve become “much less likely” to live in mixed-income neighborhoods than poor families.

Growing income inequality is driving this increasing segregation. With the income gap between the rich and everyone else expanding, the two sociologists note, mixed-income neighborhoods “have grown rarer,” and affluent and poor neighborhoods “much more common.”

Average Americans, for their part, are paying a heavy price for this growing segregation. The more isolated the rich become, the more they withdraw into their own private worlds and the less interest they have in supporting public services that can benefit the wider community.

Growing inequality and income segregation impact us on a deeper level as well. The more unequal we become, observes University of Maryland political scientist Eric Uslaner, the less we feel we have “much in common” with people unlike us.

Between 1968 and 2006, Uslaner’s research shows, the share of Americans who believe that “most people can be trusted” dropped from 56 to 34 percent. “Such overarching pessimism,” he points out, shreds social cohesion and invites political polarization. Finding “common ground” becomes ever more difficult.

Into this doom and gloom, Stanford historian Richard White has just brought some egalitarian sunshine. Once upon a time, White writes in a fascinating new Boston Review essay, most Americans lived in much more equal circumstances.

In the 1860 Illinois of Abraham Lincoln, for instance, “bricklayers, lawyers, stable owners, and managers lived in the same areas and were not much separated by wealth.”

Back then, White explains, “making it,” meant earning an income sufficient “to support a family and have enough in reserve to sustain it through hard times at an accustomed level of prosperity.”

“The idea of having enough,” adds White, “frequently trumped the ambition for endless accumulation.”

In other words, nothing in the American “character” hardwires us to chase mindlessly after grand fortune — or accept income segregation.