But false prophets also arose among the people, just as there will be false teachers among you, who will secretly bring in destructive opinions. They will even deny the Master who bought them--bringing swift destruction on themselves. (2 Pet 2:1, NRSV)
For certain intruders have stolen in among you, people who long ago were designated for this condemnation as ungodly, who pervert the grace of our God into licentiousness and deny our only Master and Lord, Jesus Christ. (Jude 4, NRSV)
Some Trinitarians are guilty of engaging in equivocation about many terms in the New Testament, such as θεος, κυριος, and in the case of Jude 4 and 2 Pet 2:1, δεσπότης. Commenting on δεσπότης in these passages, we read the following in the Theological Dictionary of the New Testament:
Jesus as δεσπότης: A completely new feature is the description of Jesus as δεσπότης in Jd. 4: την τοῦ θεοῦ ἡμῶν χάριτα μετατιθέντες εἰς ἀσέλγειαν καὶ τὸν μόνον δεσπότην καὶ κύριον ἡμῶν Ἰησοῦν Χριστὸν ἀρνούμενοι and 2 Pt. 2:1: ψευδοδιδάσκαλοι οἵτινες παρεισάξουσιν αἱρέσεις ἀπωλείας καὶ τὸν ἀγοράσαντα αὐτοὺς δεσπότην ἀρνούμενοι. In both passages, which are undoubtedly interrelated, the expression is used against errorists. These are distinguished in 2 Pt. 2:1 by their rejection of the δεσπότης, Jesus. In Jd. 4 it is just possible that we have a twofold formula, the monotheistic confession of one δεσπότης and then that of Jesus, who is here rejected. Yet if we interpret Jd. 4 in the light of 2 Pt. 2:1, we cannot accept this view and must see a single construction. We are again surprised by the proximity of αγοραζειν and δεσπότης; from Pauline usage we should have expected κυριος. Yet the description of Jesus as δεσπότης is supported by the use of δεσποσυναι for later members of His family in Eus. Hist. Ecc., I.7.14. perhaps δεσπότης is here used rather than κυριος to suggest the function of Jesus as the One who commands and exercises influence and power. To Him there corresponds an αγορασας which emphasises His right to His own in virtue of His saving act (2 Pt. 2:1: à αγοραζω, I.124). This would fit the context. The errorists’ conduct is à ασελεγεια and one of the charges against them is that they do not acknowledge Jesus in practice as the One whose will they must take as their guide. If this is so we have here a linguistic and material parallel to Jos. Bell., 7, 418 f.. (à 45), although in negative form.
This explanation is more likely than that which assumes from the common usage that δεσπότης sets Jesus alongside God as the Almighty. If this were true, it would imply a strong intrusion of abstract Hellenistic thought into Christology (found in the post-apost. Fathers, e.g., 1 Cl., 33, 1 etc.). Tempting though this suggestion may be, we should reject it in view of the context, and also on the basis of the interpretation of Jd. 4 by 2 Pt. 2:1. (Theological Dictionary of the New Testament 2:48-49)
In other words, Jesus as our only δεσπότης (and in these instances, κυριος, too) denotes Christ bring our only saviour as a result of his atoning sacrifice.
On John 17:3 and θεος, see James McGrath’s short critique of a Trinitarian apologist and their gymnastics to get around the implications of this verse.