to make a formal, usually public, promise that you will do something
pledge something to something/somebody
Moore pledged $100,000 to the orchestra at the fund-raising dinner.
pledge to do something
The new governor pledged to reduce crime.
Herrera pledged that his company will give aid to schools.
pledge (your) support/loyalty/solidarity etc
He pledged his cooperation.
pledge yourself to (do) something
Trade unions pledged themselves to resist the government plans.
to make someone formally promise something:
make somebody promise
Employees were pledged to secrecy.
to leave something with someone as a pledge1 (3)
to promise to become a member of a fraternity or sorority at an American university