To cotton on is to finally understand what is going on. Cotton on at last.
The delay is built in, since nobody is said to cotton on immediately. It is informal and British, and it usually means catching up with what everybody else already knew.
1phrasecotton onTo finally understand what is going on.
“It took him a month to cotton on to what the job actually was.”
cotton on is a phrase.
Practised in Phrasal Verbs