"And this occurred because of false brethren secretly brought in (who came in by stealth to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage)..." (Gal. 2:4)

The word "stealth" (in the above verse, NKJV) means "having or providing the capacity to evade detection; e.g, a thief, or an airplane." (Webster). The "stealth bomber" has the ability to evade radar and from this its gets its name. Error can slip in by stealth, secretly and undetected. Peter warned, "But there were also false prophets among the people, even as there will be false teachers among you, who will secretly bring in destructive heresies..." (2 Pet. 2:1)