1. noun /ˈplʌm.ət/
a) A piece of lead attached to a line, used in sounding the depth of water.
Ill sink him deeper than eer plummet sounded. -Shak.
b) A plumb bob or a plumb line.
His parachute was shot half away, and if hed jumped he would have fallen like a plummet.
2. verb /ˈplʌm.ət/
After its ascent, the arrow plummeted to earth.
Wikipedia foundation.