tier vs tier up

tier and tier up both are nouns.

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

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

tier (noun)	tier up (noun)
one of two or more layers one atop another	a worker who ties something
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