Still waters run deep is a proverb of Latin origin now commonly taken to mean that a placid exterior hides a passionate or subtle nature. Formerly it also carried the warning that silent people are dangerous, as in Suffolk's comment on a fellow lord i

Still waters run deep The quiet people can be the smartest and wisest. That is water under a bridge It is in the past now. The drop that makes a vase overflow Something is no longer bearable. They are like water and fire/ They are like devil and holy wate

"Still waters run deep". It means that quiet people can be very knowledgeable or wise. I used this phrase with my husband the other day and he said it was weird, archaic, and exclusive to the South.