Third degree

To give someone the third degree is to subject them to intense interrogation and the expression is American from the late 19th century. Since The Middle Ages, however, many things were classified by degrees where the third degree was always the highest or most intense level. For example, in Freemasonry, the third degree was the highest level and aspirants to this level were subject to intense cross-questioning. This practice was noted from the late 18th century and is thought to be the origin of today’s meaning. Third degree burns are also the highest level of burns.