Origins
The word 'shear' descends from Old English 'sceran,' meaning 'to cut,' from Proto-Germanic *skeraną, from the Proto-Indo-European root *(s)ker-, meaning 'to cut.' This PIE root, with its optional initial 's-' (called an 's-mobile'), is one of the most productive cutting-roots in the language family, generating an enormous family of words across every branch.
The primary meaning of 'shear' has always been agricultural: to cut the wool from a sheep with shears (large scissors). Sheep-shearing is one of the oldest pastoral activities, practiced since the domestication of wool-bearing sheep around 10,000 years ago. In many cultures, shearing was a communal event — a festival of labor, skill, and socializing. The Australian outback tradition of sheep-shearing competitions persists to this day.
The tool 'shears' (plural, like 'scissors') preserves the word in its most concrete form. Shears are large cutting implements used for sheep, hedges, metal, and fabric. The plural form (always 'shears,' never 'a shear' for the tool) reflects an old pattern in English where instruments with two blades or handles take the plural: shears, scissors, pliers, tongs, trousers.
Proto-Indo-European Roots
The PIE root *(s)ker- produced a vast English word family. 'Share' originally meant 'a cut portion' — your share of something is your cut. 'Ploughshare' is the cutting blade of a plough. 'Short' means 'cut off' — something short has been cut down. 'Shirt' and 'skirt' are doublets, both from Proto-Germanic *skurtijō (a short or cut garment): 'shirt' entered from Old English, 'skirt' was borrowed from Old Norse, and the two diverged into different garments. 'Score' originally meant 'a cut' or 'a notch' — tallies were kept by cutting notches in sticks, and a 'score' (twenty) was a group of twenty notches. 'Scar' is a mark left by cutting. 'Shore' may be the land that has been 'cut' or 'shorn' by the sea.
Through Latin 'curtus' (cut short, shortened), the same PIE root gave 'curt' (rudely brief — cut short), 'curtail' (to cut short), and (through the diminutive 'curtīna') 'curtain' (a piece of cut cloth). Through Greek 'keírein' (to cut, to shear): 'keratin' (the protein of hair, nails, and wool — the stuff that gets cut in shearing).
In engineering and physics, 'shear' has a technical meaning: a force that acts parallel to a surface, causing layers to slide past each other. 'Shear stress,' 'shear strain,' and 'shear force' are fundamental concepts in materials science and structural engineering. A 'shear wall' resists lateral forces in a building. 'Wind shear' describes a sudden change in wind speed or direction, dangerous to aircraft. In each technical usage, the core metaphor of cutting — a force that separates or displaces adjacent layers — is preserved.
Figurative Development
The past tense of 'shear' has two forms: 'sheared' (regular) and 'shorn' (irregular, preserving the old strong verb pattern). 'Shorn' survives mainly in figurative and literary contexts: 'shorn of power,' 'shorn of dignity,' 'a sheep shorn of its wool.' The irregular form carries a more vivid, complete sense of loss — to be shorn is to have been thoroughly stripped.