1) the commander of a camp and army, a military tribune
2) Praetorian prefect, commander of the praetorian cohorts, captain of the Roman emperor's body guard
Part of Speech: noun masculine
From G4760 and G757; a ruler of an army, that is, (specifically) a Praetorian praefect: - captain of the guard.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root στρατοπεδάρχης; click on the second column to search for that grammatical form of the root στρατοπεδάρχης; click on the third column to search for that word and grammatical form; click on the total to search for the root στρατοπεδάρχης.