Crossword puzzle clue "laborer used for underground work"

Laborer used for underground work?

Underground laborer

Opus ___ (Catholic teaching also called "the Work, work work work work")

Mexican laborer doing seasonal work in the U.S.

Laborer doing menial work

Underground pit that contains a black rock used for energy: 2 wds.

Underground source of the only letters used in today's puzzle (naturally, this answer is missing EWYOKITYTII)

(n.) a spinning device used in underground laboratories