plumb the depths of

: a lead weight attached to a line and used to indicate a vertical direction

: straight down or up : vertically

: to a complete degree : absolutely

: in a direct manner : exactly

: to weight with lead

: to measure the depth of with a plumb

: to examine minutely and critically

: exactly vertical or true

: thorough, complete

: a deep place in a body of water

: a part that is far from the outside or surface

: abyss