A level vs tier

A level and tier both are nouns.

Word	Noun	Adjective	Verb	Adverb
A level	Yes	No	No	No
tier	Yes	No	No	No

As nouns, tier is a hypernym of A level; that is, tier is a word with a broader meaning than A level:

A level: the advanced level of a subject taken in school (usually two years after O level)
tier: a relative position or degree of value in a graded group

Other hypernyms of A level include grade, level.

A level (noun)	tier (noun)
the advanced level of a subject taken in school (usually two years after O level)	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