[1] : WordNet (r) 2.0

cotton on
     v : understand, usually after some initial difficulty; "she
         didn't know what her classmates were plotting but finally
         caught on" syn: catch on, get wise, get onto, tumble,
          latch on, twig, get it
see also:
catch on get wise get onto tumble latch on twig 
get it 

Cotton >> C Words
Cotton, definition of term: Cotton
cotton_pag1.html

Cotton Wool >> C Words
Cotton Wool, definition of term: Cotton Wool
cotton+wool_pag1.html

Cotton Gin >> C Words
Cotton Gin, definition of term: Cotton Gin
cotton+gin_pag1.html

Cotton Grass >> C Words
Cotton Grass, definition of term: Cotton Grass
cotton+grass_pag1.html