0 to become fashionable or popular: --
1 to understand, especially after a long time: --
He doesn't take hints very easily, but he'll catch on (to what you're saying) eventually.
2 to become fashionable or popular: --
Why did the electronic gadget catch on so fast?
3 to understand: --
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
Vi kan slutföra det steg för steg hur lång vägen än är och den kan inte slutföras hur kort vägen än är om du inte ens markerar ditt fotavtryck.