pigeon pea vs shrub

pigeon pea and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
pigeon pea	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of pigeon pea; that is, shrub is a word with a broader meaning than pigeon pea:

pigeon pea: tropical woody herb with showy yellow flowers and flat pods; much cultivated in the tropics
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of pigeon pea include bush.

pigeon pea (noun)	shrub (noun)
small highly nutritious seed of the tropical pigeon-pea plant	a low woody perennial plant usually having several major stems
tropical woody herb with showy yellow flowers and flat pods; much cultivated in the tropics