The greatest stress that a material is capable of sustaining without deviation from a linear relationship of stress to strain.

The greatest stress that the material is capable of sustaining without a deviation from the law of proportionality of stress to strain. (Hooke’s Law)

The maximum stress at which strain remains directly proportional to stress; the upper end of the straight-line portion of the stress-strain or load-elongation curve.

The point on a stress-strain curve where the linear relationship between stress and strain ends and usually coincides with the material yield point.

Highest stress at which stress is directly proportional to strain. It is the highest stress at which the curve in a stress-strain diagram is a straight line. Proportional limit is equal to elastic limit for many metals.