Destroying the soul; ruining the spiritual nature.
The Century Dictionary (Public Domain)
Use "soul-killing" in a sentence
"Mark - I wish I could believe you (and I will watch again) but the soul-killing moment at the end only works because Teddy knows what he is and chooses lobotomy anyway."
"When he speaks on the debt negotiations, he is not only extremely boring, with airy and bromidic language—really they are soul-killing, his talking points—but he never seems to be playing it straight."
"His brother, Scott, awakens from a pot-addled adolescence to a soul-killing job, a regrettable marriage, and a vinyl-sided tract house in the suburbs."