Another phrase from the Frenemy episode of NPR’s This American Life. A lexiconical gap is the name given to an absence of a necessary word in a language. Linguistics suggests that if two words ever become fully synonymous, both in their literal and semantic meetings, one word will disappear. It is a free marketplace of ideas philosophy. However, the inverse doesn’t seem to be true. Just because a word is needed, doesn’t mean it will appear.
The best example offered is that in our English we have a word for a child who lost his parents (an orphan), a woman who lost her spouse (a widow), but we have no word for a parent who lost a child. This is a lexiconical gap.