N. limit, boundary, bounds, confine, enclave, term, # bourn, verge, curbstone, but, pale, reservation, termination, terminus, stint, frontier, precinct, marches, backwoods, boundary line, landmark, line of demarcation, line of circumvallation, pillars of hercules, rubicon, turning point, ne plus ultra, sluice, floodgate

Adj. definite, conterminate|, conterminable, terminal, frontier, bordering

Adv. thus far, thus far and no further

Phr. stick to the reservation, go beyond the pale, special