What is the definition of qadar linguistically and Islamically?

In language, "al-qadar" (Divine Decree/Predestination) is a verbal noun from "qaddara" (to destine/measure) – "yuqaddiru taqdiran," or a verbal noun from "qadara" (to be able/to measure) – "yaqdiru qadran." In Islamic law, it refers to what Allah decrees and ordains concerning affairs.