precession vs precedency

precession and precedency both are nouns.

Word	Noun	Adjective	Verb	Adverb
precession	Yes	No	No	No
precedency	Yes	No	No	No

As nouns, precession and precedency are synonyms defined as:

precession and precedency: the act of preceding in time or order or rank (as in a ceremony)

Other synonyms of precession include precedence.

precession (noun)	precedency (noun)
the act of preceding in time or order or rank (as in a ceremony)	the act of preceding in time or order or rank (as in a ceremony)
the motion of a spinning body (as a top) in which it wobbles so that the axis of rotation sweeps out a cone	preceding in time
	status established in order of importance or urgency