Have a chat to catch up
I believe the answer is:
gab
'have a chat' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'catch up' is the wordplay.
'catch' becomes 'bag' (bagging is a kind of catching).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'bag' reversed gives 'GAB'.
'to' is the link.
Can you help me to learn more?
(Other definitions for gab that I've seen before include "Talk a lot" , "Talk at length, chatter" , "The Irish are said to have the gift of it" , "gossip" , "rabbit" .)