thresh·old 
/ˈθrɛʃˌhoʊld/ noun
plural thresh·olds /ˈθrɛʃˌhoʊld/ noun [count] 1 : a piece of wood, metal, or stone that forms the bottom of a door and that you walk over as you enter a room or building
▪ He stepped across the threshold. ▪ When they were married he carried her over the threshold. [=he picked her up and carried her into their home when they entered it together for the first time] 2 : the point or level at which something begins or changes
▪ If your income rises above a certain threshold, your tax rate also rises. ▪ sounds that are above/below the threshold of hearing [=sounds that are too high/low to be heard] ▪ I have a low threshold for boredom. [=I get bored easily] ▪ He has a high pain threshold. [=he does not feel pain as easily as other people]
▪ He stepped across the threshold. ▪ When they were married he carried her over the threshold. [=he picked her up and carried her into their home when they entered it together for the first time]
▪ If your income rises above a certain threshold, your tax rate also rises. ▪ sounds that are above/below the threshold of hearing [=sounds that are too high/low to be heard] ▪ I have a low threshold for boredom. [=I get bored easily] ▪ He has a high pain threshold. [=he does not feel pain as easily as other people]
on/at the threshold
: at the beginning of something or very close to something (such as a new condition, an important discovery, etc.) — usually + of ▪ young people on the threshold of adulthood ▪ We are (standing) at the threshold of a great adventure.
