Why do words like "expectorate" sound more posh than words like "spit"?

Solution 1:

The "more posh" words are usually Latin (occasionally Greek) in origin. The more common sounding words are from original Anglo-Saxon (I'm sure a real linguist knows more). The more educated classes tended to be more likely to use Latin and other foreign terms, while the less educated classes used the vernacular (i.e. the vulgar, common language) of the day.

Solution 2:

They're longer and more difficult to spell and pronounce. Thus, they require higher education.

If you utilize (use) polysyllabic vocabulary (words), you will indubitably (without fail) sound more posh.

Solution 3:

There is actually an interesting term for this.

inkhorn (adj): ostentatiously learned: pedantic.

Ironically enough, I'd consider the word itself to be a good example of an inkhorn term. It was coined during the Renaissance to criticize learned writers who favored borrowed works from Latin and Greek over "vulgar" English alternatives.

Solution 4:

If you want to write words people can feel, use little ones. "The bad news was like a kick in the gut." "The disturbing information caused the individual's intestines to turn queasy."