tailspin

As nouns the difference between tailspin and plummet

is that tailspin is the rapid, uncontrollable descent of an aircraft in a steep spiral while plummet is (archaic) a piece of lead attached to a line, used in sounding the depth of water.

As a verb plummet is

to drop swiftly, in a direct manner; to fall quickly.

As nouns the difference between tailpin and tailspin

is that tailpin is the centre in the spindle of a turning lathe while tailspin is the rapid, uncontrollable descent of an aircraft in a steep spiral.

As nouns the difference between taxonomy and tailspin

is that taxonomy is the science or the technique used to make a classification while tailspin is the rapid, uncontrollable descent of an aircraft in a steep spiral.