catch_on
1. [ verb ] understand, usually after some initial difficulty
Synonyms: get_it get_onto cotton_on twig latch_on get_wise tumble
Examples:

"She didn't know what her classmates were plotting but finally caught on"

Related terms: get_the_picture
2. [ verb ] become popular
Examples:

"This fashion caught on in paris"

Related terms: change
Similar spelling:   catching
  catchment
  Catchings
  catechumen