to create or develop something
Example:
- She's built up a very successful business.
- These finds help us build up a picture of life in the Middle Ages.
- I am anxious not to build up false hopes (= to encourage people to hope for too much).
- The gallery has built up a fine collection of contemporary art.
- We’ve built up good relationships with our clients.
to make something higher or stronger than it was before
Example:
- The sea defences have been built up to ensure that such a disaster will not strike again.