Originally, the distance between an adult man's arms stretched out away from the sides of his torso so that they make a straight line perpendicular to his body, measured from the tips of the longest fingers of each hand, generally reckoned to be six feet (about 1.8 metres); subsequently used as a unit for water depth but now generally replaced by the metre.
Depth of insight; mental reach or scope.
An unspecified depth.
To encircle (someone or something) with outstretched arms; specifically, to measure the circumference or (rare) length of something.
To measure a depth; to sound.
To conduct an examination or inquiry; to investigate.
To measure the depth of (water); to take a sounding of; to sound.
Often followed by out: to deeply understand (someone or something); to get to the bottom of.