annual vs plant life

annual and plant life both are nouns.

Word	Noun	Adjective	Verb	Adverb
annual	Yes	Yes	No	No
plant life	Yes	No	No	No

As nouns, plant life is a hypernym of annual; that is, plant life is a word with a broader meaning than annual:

annual: (botany) a plant that completes its entire life cycle within the space of a year
plant life: (botany) a living organism lacking the power of locomotion

Other hypernyms of annual include flora, plant.

annual (noun)	plant life (noun)
a reference book that is published regularly once every year	(botany) a living organism lacking the power of locomotion
(botany) a plant that completes its entire life cycle within the space of a year

annual (adjective)	plant life (adjective)
completing its life cycle within a year
occurring or payable every year