Fossil word

A fossil word is a word that is broadly obsolete but remains in current use due to its presence within an idiom, word sense, or phrase. An example for a word sense is 'ado' in 'much ado'. An example for a phrase is 'in point' (relevant), which is retained in the larger phrases 'case in point' (also 'case on point' in the legal context) and 'in point of fact', but is rarely used outside of a legal context.