procedure vs stiffening

procedure and stiffening both are nouns.

Word	Noun	Adjective	Verb	Adverb
procedure	Yes	No	No	No
stiffening	Yes	No	No	No

As nouns, stiffening is a hyponym of procedure; that is, stiffening is a word with a more specific, narrower meaning than procedure:

procedure (noun)	stiffening (noun)
a particular course of action intended to achieve a result	the act of becoming stiff
a mode of conducting legal and parliamentary proceedings	the process of becoming stiff or rigid
a process or series of acts especially of a practical or mechanical nature involved in a particular form of work
a set sequence of steps, part of larger computer program