varna vs shudra

varna and shudra both are nouns.

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

As nouns, shudra is a hyponym of varna; that is, shudra 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)
shudra: the lowest of the four varnas: the servants and workers of low status

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

varna (noun)	shudra (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