Propraetor was originally a magistrate with imperium who acted as a substitute for the praetor, but during the period of the Roman Republic, the propraetor became the term for a former magistrate whose year was extended, or a praetor appointed as a substitute for the regularly elected praetor. Like proconsuls, propraetors were sent by the Senate to provinces to serve as governors following their year-long term as magistrate.
Adolf Berger's Encyclopedic Dictionary of Roman Law, 1953.
Roman Magistrates With Imperium
Alternate Spellings: pro praetor
Examples:
"Praetors and ex-praetors could expect important and sometimes lucrative provincial assignments." P. 163, The Last Generation of the Roman Republic, by Erich S. Gruen.
Like praetors becoming propraetors, consuls became proconsuls.