This came up in another topic.
What he meant was “Now I get it !” “Now I understand the term”.
To “catch on” cannot be applied to understanding a word.
It means: “understand the situation”, or “understand why things are happening in a certain way”, or “how serious the situation is”.
It is similar to the expression “Cop on” which mean “be sensible” or “be street-wise”
Here in Ireland we might tell someone to: “have some cop-on”
It is normally used without saying exactly what has to be understood. That can be taken as understood. If it has to be explained the person will never “catch on”.
One might say to someone “Catch on!” or “Catch on to yourself” meaning “Be aware of the problems here”, or “Be responsible!”
Here in Ireland one might say “Catch yourself on” .
Can anybody tell me is it used this way outside of Ireland ?
“Catch on” can also mean “become popular”.
Yu-Gi-Oh cards have really caught on among kids here in Dublin(speaking very locally).
Native Hiberno English speaker