Definitions for "Fossilisation"
The process by which a fossil is formed.It is unusual for organisms to be preserved complete and unaltered: generally, the soft parts decay and the hard parts undergo various degrees of change.
the process of fossilizing a plant or animal that existed in some earlier age; the process of being turned to stone
The processes which allow a remnant or trace of a living organism to be preserved. This may be simple burial in sediment, or may involve the replacement of the organism by sediment or mineral
becoming inflexible or out of date
Learners of foreign languages often reach a certain level or plateau of competence and stick there: their language is still not close to the target of sounding like a native speaker, and seems not to be improved by further contact with teachers or native speakers: it's fossilised.