lilac vs shrub

lilac and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
lilac	Yes	Yes	No	No
shrub	Yes	No	No	No

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

lilac: any of various plants of the genus Syringa having large panicles of usually fragrant flowers
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of lilac include bush.

lilac (noun)	shrub (noun)
any of various plants of the genus Syringa having large panicles of usually fragrant flowers	a low woody perennial plant usually having several major stems

lilac (adjective)	shrub (adjective)
of a pale purple color