A Hebrew verb meaning to prosper, succeed, be profitable, advance, rush (upon). In the Qal stem, it means to rush or advance forcefully. In the Hiphil, it means to cause to prosper, make successful. It describes both physical rushing (the Spirit rushing upon someone) and the abstract concept of success and prosperity.
This word connects divine empowerment with observable success. When the Spirit of the LORD 'rushed upon' (tsalach) Samson (Judges 14:6) or Saul (1 Samuel 10:6), the same word that means 'prosper' is used for the Spirit's powerful coming. This suggests that true prosperity comes from the Spirit's empowerment, not human effort. In Joshua 1:8, meditating on Torah makes one's way 'prosperous' (tsalach) — prosperity is a fruit of obedience. Isaiah 55:11 declares that God's word will prosper in what it was sent to do — divine speech always accomplishes its purpose. The prosperity theology of Scripture is not material wealth but Spirit-empowered fruitfulness in God's purposes.