a. The foot of a doorway crossed in entering a house or room.
synonyms: doorstep, sill, doorsill, doorway, entrance, entry, way in, door, gate, gateway, portal, approach
b. a point of entry or beginning.
synonyms: start, starting point, beginning, brink, verge, edge, dawn, birth, origin, inception, conception, opening, launch, inauguration, institution, initiation, debut, creation, day one
b. the magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested.
synonyms: lower limit, starting point, minimum, margin, limen