From the Suda:

“Tyrannos: The poets before the Trojan War used to name kings (basileis) tyrants, but later during the time of Archilochus, this word was transferred to the Greeks in general, just as the sophist Hippias records. Homer, at least, calls the most lawless man of all, Ekhetos, a king, not a tyrant. Tyrant is a a name that derives from the Tyrrenians because these men were quite severe pirates.* None of the other poets uses the name tyrant in any of their works. But Aristotle in the Constitution of the Cumaeans says that tyrants were once called aisumnêtai, because this name is a bit of a euphemism.”

Τύραννος: οἱ πρὸ τῶν Τρωϊκῶν ποιηταὶ τοὺς βασιλεῖς τυράννους προσηγόρευον, ὀψέ ποτε τοῦδε τοῦ ὀνόματος εἰς τοὺς Ἕλληνας διαδοθέντος κατὰ τοὺς Ἀρχιλόχου χρόνους, καθάπερ Ἱππίας ὁ σοφιστής φησιν. Ὅμηρος γοῦν τὸν πάντων παρανομώτατον Ἔχετον βασιλέα φησί, καὶ οὐ τύραννον. προσηγορεύθη δὲ τύραννος ἀπὸ Τυρρηνῶν: χαλεποὺς γὰρ περὶ λῃστείας τούτους γενέσθαι. οὐδεὶς δὲ οὐδὲ ἄλλος τῶν ποιητῶν ἐν τοῖς ποιήμασιν αὐτοῦ μέμνηται τὸ τοῦ τυράννου ὄνομα. ὁ δὲ Ἀριστοτέλης ἐν Κυμαίων πολιτείᾳ τοὺς τυράννους φησὶ τὸ πρότερον αἰσυμνήτας καλεῖσθαι. εὐφημότερον γὰρ ἐκεῖνο τὸ ὄνομα. ὅτι καὶ ἕτεροι ἐτυράννησαν, ἀλλ’ ἡ τελευταία καὶ μεγίστη κάκωσις πάσαις ταῖς πόλεσιν ἡ Διονυσίου τυραννὶς ἐγένετο.

For Aristotle’s distinctions, see Politics, book 3 (1285a)

*According to Louise Hitchcock and Aren Maeir (“Yo-ho, Yo-ho: A Seren’s Life For me.” World Archaeology 46:4, 624-640) the Philistines used the word seren to mean leader; this word may have been related to Hittite tarwanis and was possibly circulated by the ‘sea peoples’. Greek tyrannos may have developed from this. Chaintraine notes that the etymology of turannos is unclear but that it may be related to Etruscan turan or Hittite tarwana.

Hesychius:  anangkomonarkhos “monarch-by-force”: a tyrant

ἀναγκομόναρχος· ὁ τύραννος

Etymologicum Magnum

“This is likely formed from Tursennians*. Or it derives from Gyges who was from a Turran city in Lykia, and he was the first one who was a tyrant. Others claim it is from truô [“to distress, wear out, afflict”], that it was truanos and that the rho and nu switched places through pleonasm. Ancients used to use the word Turannos for kings. There was a time when they used a call the tyrant ‘king’.

Τύραννος: ῎Ητοι ἀπὸ τῶν Τυρσηνῶν· ὠμοὶ γὰρ οὗτοι· ἢ ἀπὸ Γύγου, ὅς ἐστιν ἀπὸ Τύρρας πόλεως Λυκιακῆς, τυραννήσαντος πρῶτον. ῎Αλλοι δὲ ἀπὸ τοῦ τρύω, τὸ καταπονῶ, τρύανος· καὶ ὑπερβιβασμῷ τοῦ ρ, τύραννος, κατὰ πλεονασμὸν τοῦ ν. Τύραννον δὲ οἱ ἀρχαῖοι καὶ ἐπὶ βασιλέως ἔτασσον· ἔσθ’ ὅτε δὲ καὶ τὸν τύραννον βασιλέα ἔλεγον.

*A name for Etruscans

s.v. Αἰσυμνητήρ

“An aisiomêtês is one who has proper plans. A tyrant is the opposite.”

ὁ αἰσιομήτης, ὁ αἴσια βουλευόμενος· ὁ γὰρ τύραννος τοὐναντίον.

s.v. Βασιλεύς

“For, a king must truly do noble things. One who does evil, he’s a tyrant.”

δεῖ γὰρ ἀληθῶς βασιλέα καλοποιεῖν· ὁ δὲ κακοποιῶν, τύραννος

 

Etymologicum Gudianum

“Tyranny: It differs from a kingship and a tyrant is different from a king. For a kingship is something that exercises power according the law. But a tyranny is a force without reason, following its own law. A king is someone who rules according to just laws; but a tyrant, who can never rule justly nor without the boundaries of the law, he steps outside of the laws.”

Tyrannos: from some tyrant, the one who first ruled badly, from the city of Tyre. It means two things: a kind and the man as a tyrant.”

Τυραννὶς, βασιλείας διαφέρει, καὶ τύραννος βασιλέως· βασιλεῖα μὲν γάρ ἐστι κατὰ νόμους ἄρχουσα ἐξουσία τίς· τυραννὶς δὲ ἡ ἄλογος ἐξουσία, αὐτωνομίᾳ χρωμένη· βασιλεύς ἐστιν ὁ κατὰ νόμους δικαίους ἄρχων· τύραννος δὲ, ὁ μήτε δικαίως ἄρχων, μήτε νομίμως, ἀλλὰ καὶ τοὺς νόμους ἐκπατῶν.

Τύραννος, ἀπὸ τυράννου τινὸς, πρώτου κακῶς διακειμένου, ἀπὸ Τύρου τῆς πόλεως· σημαίνει δὲ δύο, τὸν βασιλέα καὶ τὸν ἄνθρωπον τύραννον.

 

Aristotle, Politics 1285a

“Citizens guard their kings with arms; foreigners protect tyrants. This is because kings rule according to the law and with willing citizens while tyrants rule the unwilling. As a result, kings have guards from their subjects and tyrants keep guards against them.”

οἱ γὰρ πολῖται φυλάττουσιν ὅπλοις τοὺς βασιλεῖς, τοὺς δὲ τυράννους ξενικόν: οἱ μὲν γὰρ κατὰ νόμον καὶ ἑκόντων οἱ δ᾽ ἀκόντων ἄρχουσιν, ὥσθ᾽ οἱ μὲν παρὰ τῶν πολιτῶν οἱ δ᾽ ἐπὶ τοὺς πολίτας ἔχουσι τὴν φυλακήν.

Od. 18.83-87

“If this one defeats you and proves stronger,
I will send you to the shore, throw you in a black ship,
And ship you off to king Ekhetos, the most wicked man of all.
He will cut off your nose and ears with pitiless bronze
And after severing your balls, he will feed them raw to his dogs.”

αἴ κέν σ’ οὗτος νικήσῃ κρείσσων τε γένηται,
πέμψω σ’ ἤπειρόνδε, βαλὼν ἐν νηῒ μελαίνῃ,
εἰς ῎Εχετον βασιλῆα, βροτῶν δηλήμονα πάντων,
ὅς κ’ ἀπὸ ῥῖνα τάμῃσι καὶ οὔατα νηλέϊ χαλκῷ
μήδεά τ’ ἐξερύσας δώῃ κυσὶν ὠμὰ δάσασθαι.”

Cf. 22.474-477 where Odysseus and Telemachus have this done to the cow-herd, Melanthios:

“They took Melanthios out through the hall and into the courtyard.
They cut off his nose and ears with pitiless bronze.
Then they cut off his balls and fed them raw to the dogs;
And they cut off his hands and feet with an enraged heart.”

ἐκ δὲ Μελάνθιον ἦγον ἀνὰ πρόθυρόν τε καὶ αὐλήν·
τοῦ δ’ ἀπὸ μὲν ῥῖνάς τε καὶ οὔατα νηλέϊ χαλκῷ
τάμνον μήδεά τ’ ἐξέρυσαν, κυσὶν ὠμὰ δάσασθαι,
χεῖράς τ’ ἠδὲ πόδας κόπτον κεκοτηότι θυμῷ.

Ekhetos is mentioned again at 18.116 and 21.308. The scholia repeat how cruel he is; but most seem to believe that he was made up by Homer.