n. The plank, stone, or piece of timber which lies at the bottom of a door, or under it, particularly the door of a dwelling-house, church, temple, or other building; a door-sill; hence, entrance; gate; door.n. Hence, the place or point of entering or beginning; outset: as, he is now at the threshold of his argument.n. In psychology, the limit below which a given stimulus,' or the difference between two stimuli, ceases to be perceptible. Compare schwelle.