In physics|lang=en terms the difference between shear and viscous
is that
shear is (physics) a force that produces a shearing strain while
viscous is (physics) of or pertaining to viscosity.
As adjectives the difference between shear and viscous
is that
shear is while
viscous is having a thick, sticky consistency between solid and liquid.
As a verb shear
is to cut, originally with a sword or other bladed weapon, now usually with shears, or as if using shears.
As a noun shear
is a cutting tool similar to scissors, but often larger.