In this week's Shabbat B'Shabbato Eliyahu Netanel discusses the origin of the word סרן seren (army captain in Modern Hebrew). He mentions that it appears 22 times in the Tanach - once as an axle (Malachim I 7:30), and the remaining times as Philistine princes. He quotes the Ben Yehuda dictionary as saying that there are those who say the origin is in the Greek Turannos, and that the Targum translates the term as טוּרְנֵי פלשתאֵי.
He goes on to quote Kutscher's chapter on the word, where he claims that it derives from the Greek tyrannos - meaning "lord, master", and gives us the English word tyrant. Kutscher points out that there seems to be much evidence that the Philistines were connected to the Greeks. However, in his book (not quoted by Netanel) Kutscher writes that the word tyrannos is not likely of Greek origin, but borrowed by the Greeks (and the Philistines) from one of the languages spoken in Asia Minor.
Of course there are other opinions. Klein says that seren is "perhaps a dialectal of שר (prince in Hebrew)". Steinberg says that the meaning "axle" is related, for the princes are the axles upon which the kingdom revolves. And Yehuda Kil, in the Daat Mikra commentary to Shmuel I 5:8, says that perhaps seren is related to the Hittite SER, meaning "superior".