Threshold1. (n.) The plank, stone, or piece of timber, which lies under a door, especially of a dwelling house, church, temple, or the like; the doorsill; hence, entrance; gate; door.
2. (n.) Fig.: The place or point of entering or beginning, entrance; outset; as, the threshold of life.
Thesaurus Entries
French door, archway, back door, barway, beginning, border line, bound, boundary, boundary condition, boundary line, bourn, break boundary, breakoff point, brink, bulkhead, carriage entrance, ceiling, cellar door, cellarway, circumscription, commencement, compass, confine, cutoff, cutoff point, dawn, deadline, delimitation, determinant, division line, door, doorjamb, doorpost, doorsill, doorstep, doorstone, doorway, edge, end, entrance, entrance hall, entranceway, entry, entryway, extremity, finish, floor, foyer, front door, frontier, galilee, gate, gatepost, gateway, groundsel, hatch, hatchway, hedge, high-water mark, interface, limen, limit, limitation, limiting factor, line, line of demarcation, lintel, lobby, low-water mark, lower limit, march, mark, mete, mudsill, narthex, outset, point, porch, portal, porte cochere, portico, postern, propylaeum, pylon, scuttle, side door, sill, start, starting line, starting point, stile, stoa, storm door, target date, term, terminal date, terminus, time allotment, tollgate, trap, trap door, turnpike, turnstile, upper limit, verge, vestibule, window sill