When did the QT become the DL? And what is the QT?

Question

My parents say to "keep things on the QT", my students say to "keep them on the DL". I know that DL stands for "Down Low". What does QT stand for and when did this fundamental shift in language take place?

Answer 1

I was always told by the old-timers that the QT meant the "quiet touch". Doesn't really make sense to me, either.

Answer 2

q.t. means quiet ( informal ) or could also mean secret or
in convidence.