Douglas Harper's Etymology Dictionary
Wikipedia
Usage examples of "profundis".
Nick De Profundis, the company lounge lizard, has surprised everybody by changing, inside the phone booth of factory spaces here, to an energetic businessman, selling A4 souvenirs: small items that can be worked into keychains, money clips or a scatter-pin for that special gal back home, burner cups of brass off the combustion chambers, ball bearings from the servos, and this week the hep item seems to be SA 100 acorn diodes, cute little mixing valves looted out of the Tele-funken units, and the even rarer SA 102s, which of course fetch a higher price.
Four lay-brothers raised the bier, and followed a troop of priests and monks, who went first with the crucifix, chaunting a De profundis.