How do you account for words that we know but rarely use?

President Obama recently poked fun at Romney for his use of the word marvelous in describing the Republican budget proposal. Politics aside, this would seem to be an example of a word whose meaning we all know, but would be unlikely to use. Some years ago, Billy Crystal created a character on Saturday Night Live whose tag line was , “You look marvelous,” where the word was being used for comic effect.

This got me to thinking of other words that I recognize but would not likely use, like escapade, flamboyant, egregious, lest and muse. Another example that made the news was the statement, “We paean the people of Korea,” made by the officer of the ship Pueblo after it was captured by North Korea. How often do you hear the word paean being used?

So here is my question. Are these special occasion words, or are they words that are in the process of leaving the language? Are there words more likely to be used in writing than in speech?