Verb catch on has 2 senses
  1. catch on, get wise, get onto, tumble, latch on, cotton on, twig, get it - understand, usually after some initial difficulty; "She didn't know what her classmates were plotting but finally caught on"
    --1 is one way to get the picture, comprehend, savvy, dig, grasp, compass, apprehend
    Sample sentences:
    Somebody ----s
    Somebody ----s PP
  2. catch on - become popular; "This fashion caught on in paris"
    --2 is one way to
    change
    Sample sentences:
    Something ----s
    Something is ----ing PP
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