In a big redesign, there can be terminology changes and mapping to backend entities that needs to happen. What are the best practices for doing this? Also, for making documentation consistently searchable
Assuming that you haven't already done so, it would be important to go back to the data and look at the information architecture to take time and document the structure and relationships between entities.
This will form the basis for the 'what is' state of things at the, then you need to do the same for the 'to be' state of the future system and map the relationships and structures that are consistently, while coming up with new terminologies and conventions for things that are different.
The process that you go through with the mapping, when documented, will provide the template for a glossary or dictionary between the 'old' and 'new' terms.
As with most documentation, anything that is 'live' (i.e. easily accessible from a central location with up-to-date information and 'living' (i.e. it is expected to change and evolve) is going to be easiest to maintain and reference.