tier up vs tier

tier up and tier both are nouns.

Word	Noun	Adjective	Verb	Adverb
tier up	Yes	No	No	No
tier	Yes	No	No	No

As nouns, tier up and tier are synonyms defined as:

tier up (noun)	tier (noun)
a worker who ties something	one of two or more layers one atop another
	any one of two or more competitors who tie one another
	a relative position or degree of value in a graded group
	something that is used for tying
	a worker who ties something