Other forms: mucking; mucked; mucks
Muck is a goopy, muddy substance, like the muck at the bottom of a pond or the muck you clean out of the gutters on your house once a year.
You can also use muck to mean animal manure, its original, 13th-century meaning — specifically, "cow dung and vegetable matter used as manure." The definition has expanded since then to include any number of dirty, slimy substances, from the mud on the bottom of a lake to the sludge in a flooded basement. As a verb, to muck is either to remove animal waste or to spread manure on a field.