1.
If you ~ to something, you understand it, or realize that it is happening.
He got what he could out of me before I caught on to the kind of person he’d turned into...
Wait a minute! I’m beginning to ~.
PHRASAL VERB: V P to n, V P
2.
If something catches on, it becomes popular.
The idea has been around for ages without catching on.
PHRASAL VERB: V P