Adam Clarke on Psalms 34:18

A broken heart - נשברי לב nishberey Web, the heart broken to shivers.

A contrite spirit - דכאי רוח dakkeey ruach, "the beaten-out spirit." In both words the hammer is necessarily implied; in breaking to pieces the ore first, and then plating out the metal when it has been separated from the ore. This will call to the reader's remembrance Jer 23:29 : "Is not my word like as a fire, saith the Lord? And like a hammer that breaketh the rock in pieces?" The breaking to shivers, and beating out, are metaphorical expressions: so are the hammer and the rock. What the large hammer struck on a rock by a powerful hand would do, so does the word of the Lord when struck on the sinner's heart by the power of the Holy Spirit. The broken heart, and the contrite spirit, are two essential characteristics of true repentance.