precedency vs precession

precedency and precession both are nouns.

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

As nouns, precedency and precession are synonyms defined as:

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

Other synonyms of precedency include precedence.

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