The term "stress" had none of its contemporary connotations before the 1920s. It is a form of the Middle English "destresse", derived via Old French from the Latin "stringere", "to draw tight". The word had long been in use in physics to refer to the internal distribution of a force exerted on a material body, resulting in strain. In the 1920s and '30s, biological and psychological circles occasionally used the term to refer to a mental strain or to a harmful environmental agent that could cause illness.