shudra vs varna

shudra and varna both are nouns.

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

As nouns, varna is a hypernym of shudra; that is, varna is a word with a broader meaning than shudra:

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

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