Parthia = "a pledge"
1) an inhabitant of Parthia, a district of Asia, bounded on the north by Hyrcania, on the east by Ariana, on the south by Carmania Deserta, on the west by Media
Part of Speech: noun proper masculine
Probably of foreign origin; a Parthian, that is, inhabitant of Parthia: - Parthian.
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 Πάρθος; click on the second column to search for that grammatical form of the root Πάρθος; click on the third column to search for that word and grammatical form; click on the total to search for the root Πάρθος.