clear·ance 
/ˈklirəns/ noun
plural clear·anc·es /ˈklirəns/ noun 1 a : an official decision saying that someone has permission to do something [noncount] ▪ You'll have to get clearance [=approval] from management to go ahead with the project. ▪ The documents are only available to people with security clearance [=special permission given only to people who are approved to know or see secret things] from the government. [count] ▪ She has a security clearance that allows her to see the classified information.
b : official permission for an aircraft, pilot, etc., to do something [noncount] ▪ The pilot got clearance to land. ▪ That flight has not received clearance for landing/takeoff. [count] ▪ a clearance for landing/takeoff 2 : the amount of space between two things [noncount] ▪ There was only 10 inches of clearance between the car and the side of the tunnel. [count] ▪ The car has a road/ground clearance of seven inches. [=the bottom of the car is seven inches above the road/ground] ▪ a bridge with a 100-foot clearance above the water 3 [noncount] : the act or process of removing things (such as trees or old buildings) from an area
▪ the clearance of forests for farming ▪ slum clearance to make room for new housing
b : official permission for an aircraft, pilot, etc., to do something [noncount] ▪ The pilot got clearance to land. ▪ That flight has not received clearance for landing/takeoff. [count] ▪ a clearance for landing/takeoff
▪ the clearance of forests for farming ▪ slum clearance to make room for new housing
