threshold
thresh·old / ˈ[unvoicedth]reshˌ(h)ōld/ • n. 1. a strip of wood, metal, or stone forming the bottom of a doorway and crossed in entering a house or room. ∎ [in sing.] a point of entry or beginning: she was on the threshold of a dazzling career. ∎ the beginning of an airport runway on which an aircraft is attempting to land.2. the magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested: nothing happens until the signal passes the threshold | [as adj.] a threshold level. ∎ the maximum level of radiation or a concentration of a substance considered to be acceptable or safe: their water would meet the safety threshold of 50 milligrams of nitrates per liter. ∎ Physiol. & Psychol. a limit below which a stimulus causes no reaction: everyone has a different pain threshold.
