These words are comparable in their denotation of the action or effect of a force upon a person or thing. The first term, stress , designates any force or combination of forces that acts on a body or part of a body, as by pressing, pushing, pulling, stretching, compressing or twisting, and by such action tends to cause a change in the shape or size of the body acted upon. When used in reference to a person, stress indicates a condition of emotional or intellectual distress. There is a suggestion in stress of some external stimulus, such as injury, worry or shock, that exerts a compelling or constraining influence to which the person involved cannot adequately adjust: a serious gastro-intestinal disorder that was the result of the stress of anxiety and grief.

Stain when used in relation to an object, denotes the change in shape or size of that object when it is acted upon by a stress . A suggestion of the natural resistance an object makes to the action of stress is carried over to the meaning of strain when it pertains to persons. Resistance implies effort, and a person undergoing stain is subject to the physical, mental or emotional distress that severe effort entails: the constant strain of trying to make ends meet on an inadequate wage; the strain of working while suffering from a painful back ailment.

In their application to inanimate things, tension and pressure may be classified as types of stresses . Tension is an elongating stress caused by a force that pulls or stretches an object in one direction. Pressure is a kind of stress characteristically produced by fluids; its special property is that its force is the same in all directions. In designating the condition of a person, tension hints at a state of mental strain whose peculiarity is its manifestation in physical distress, as in headaches or taut muscles: a tranquillizer to reduce nervous tension after an unsuccessful job interview. Tension has come popularly to denote also any state of strained relations like that caused by conflict or hostility between persons or groups of persons: the tension existing between the U.S. and the U.S.S.R. Pressure , more than the other words in this group, specifically points to the things producing a state of strain or tension rather than to the state itself. It is a general word that can apply to anything from a minor and temporary difficulty to major, continuous misfortune: the pressure of a too-busy social schedule; job pressure ; the pressures of poverty.