Definitions:

1. to bolster or strengthen verb
   • I wanted to build up my portfolio.
2. to enlarge, develop, or increase by degrees or in stages verb
   • You should build up your savings to cover your retirement.
3. to form or accumulate steadily verb
   • The calcium in the shower kept building up.
4. to prepare oneself for a military confrontation verb
   • We are building up for the next battle.

Synonyms:

• build
• fortify
• gird
• progress