varna vs sudra

varna and sudra both are nouns.

Word	Noun	Adjective	Verb	Adverb
varna	Yes	No	No	No
sudra	Yes	No	No	No

As nouns, sudra is a hyponym of varna; that is, sudra is a word with a more specific, narrower meaning than varna:

varna: (Hinduism) the name for the original social division of Vedic people into four groups (which are subdivided into thousands of jatis)
sudra: the lowest of the four varnas: the servants and workers of low status

Other hyponyms of varna include brahman, brahmin, rajanya, vaisya, shudra.

varna (noun)	sudra (noun)
(Hinduism) the name for the original social division of Vedic people into four groups (which are subdivided into thousands of jatis)	the lowest of the four varnas: the servants and workers of low status