Fossil word

A fossil word is a word that is broadly obsolete but remains in current use due to its presence within an idiom. Fossil status can also occur for word senses and for phrases. An example for a word sense is 'navy' in 'merchant navy', which means 'commercial fleet' (although that sense of navy is obsolete elsewhere). 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.
English-language examples.
"Born fossils".
These words were formed from other languages, by elision, or by mincing of other fixed phrases.