To significantly increase a risk, investment, or other commitment; to respond to a challenge (e.g. to an opinion) by reinforcing or extending one's position rather than moderating it.
To double one's wager. In particular, it is the name of a specific doubling bet allowed in blackjack.
To withdraw or repudiate a statement or opinion formerly expressed, especially formally and publicly.
To give a new cant (slant, angle) to something, in particular railway track on a curve.