From hupo and stello; to withhold under (out of sight), i.e. (reflexively) to cower or shrink, (figuratively) to conceal (reserve) -- draw (keep) back, shun, withdraw.
KJV: For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision.
NASB: For prior to the coming of certain men from James, he used to eat with the Gentiles; but when they came, he began to withdraw and hold himself aloof, fearing the party of the circumcision.