From 'beside' and 'lead in', this compound verb emphasizes secretive introduction—smuggling in people, ideas, or practices by stealth. Classical usage included introducing allies into besieged cities secretly. Second Peter 2:1 warns of false teachers who will secretly introduce destructive heresies. The future tense projects the threat forward, while the adverbial prefix captures the covert nature—not open debate but infiltration, introducing error by stealth rather than argument.