v.1. To snag something on something: I caught the sleeve of my jacket on a branch, and it ripped.
2. To understand or figure something out: We played a practice game so that the new players could catch on before we started betting. We were slow to catch on to the swindler's tricks.
3. To become popular or fashionable: Since the time when skateboarding first caught on, there have been many improvements in wheel design.