LSJ Gloss:παρείσακτοςintroduced privilyDodson:παρείσακτοςbrought in secretlybrought in secretly, surreptitious.
TBESG:παρείσακτοςinfiltratedG:A παρ-είσ-ακτος, -ον (< παρεισάγω), brought in secretly (as spies or traitors) : Gal.2:4.† (AS)
παρεισάγω pareisagō par-ice-ag'-o From G3844 and G1521; to lead in aside, that is, introduce surreptitiouslyKJV Usage: privily bring in.