brief, little, quick, short
long
cosy/cozy, fireside, friendly, good, nice
casual, informal
quiet
interesting
private

have
We had a nice chat over a cup of tea.

chat about
a chat about his new job

chat between
a chat between the star and a journalist

chat to, chat with
I'll have a chat to John about it.
a friendly chat with a colleague

idle
They say he's already married, but it's just idle chat.

show (BrE)
line (usually chatline)

Internet, live, online
You can take part in a live online chat with the movie's director this afternoon.

forum, group, room, session, site
You can't believe all the stories you hear in Internet chat rooms.