Prof is a colloquial clipping of professor (from Latin professor 'public teacher', from profiteri 'to declare publicly, profess', from pro- 'forth' + fateri 'to acknowledge'). The historical chain includes Latin professor and Latin profiteri. The quoted older senses, "public teacher", "to declare publicly, profess", "forth", and "to acknowledge", supply the semantic anchors for prof. The formation is best read as compound and borrowed: the word prof carries its older form-history into a compact English lexical shape. In present English it is used as a noun, "an informal term for a professor". Related English forms include professor, professorial, and profess. The result is a noun whose etymology preserves both the older form and the later English specialization.