This picturesque phrase, "great swelling words," is the King James Version translation of huperonkos, which literally means "super-massive," with the implied noun "words" added because of the context.
The word is used only one other time in the New Testament, in the parallel passage in 2 Peter 2:18: "For when they speak great swelling words of vanity, they allure through the lusts of the flesh, through much wantonness, those that were clean escaped from them who live in error."
Both apostles, in context, are warning against false teachers who, after somehow obtaining positions of influence among the spiritually immature believers in the body, would then seek to lead them back into worldly ways of thinking and acting. Peter compares those who heed such words to washed sows going back to wallow in the mire (2 Peter 2:22).
Such teachers may appear very intellectual and charismatic, with their "feigned words" (2 Peter 2:3), promises of "liberty" (1 Peter 2:16), and flatteries (see text above), but it is a deadly mistake to follow them. Both Peter and Jude give various ways by which to recognize them. They may actually deny the redemptive work of Christ (2 Peter 2:1), or seek to undermine those whom God has placed in authority (2:10). Perhaps most commonly, they are interested in worldly gain or prestige for themselves (2 Peter 2:14; Jude 11). They also may practice and encourage carnal lifestyles (Jude 4).
Other characteristics of these deceptive teachers are given in these two key chapters and, by all means, young believers need to be alert to this danger, staying close to God's Word and obedient to His will. HMM