**The Collaborative International Dictionary of English v.0.48:**

Modulus \Mod"u*lus\, n.; pl. Moduli. [L., a small measure. See
Module, n.] (Math., Mech., & Physics)
A quantity or coefficient, or constant, which expresses the
measure of some specified force, property, or quality, as of
elasticity, strength, efficiency, etc.; a parameter.
[1913 Webster]
Modulus of a machine, a formula expressing the work which a
given machine can perform under the conditions involved in
its construction; the relation between the work done upon
a machine by the moving power, and that yielded at the
working points, either constantly, if its motion be
uniform, or in the interval of time which it occupies in
passing from any given velocity to the same velocity
again, if its motion be variable; -- called also the
efficiency of the machine. --Mosley. --Rankine.
Modulus of a system of logarithms (Math.), a number by
which all the Napierian logarithms must be multiplied to
obtain the logarithms in another system.
Modulus of elasticity.
(a) The measure of the elastic force of any substance,
expressed by the ratio of a stress on a given unit of the
substance to the accompanying distortion, or strain.
(b) An expression of the force (usually in terms of the
height in feet or weight in pounds of a column of the
same body) which would be necessary to elongate a
prismatic body of a transverse section equal to a given
unit, as a square inch or foot, to double, or to compress
it to half, its original length, were that degree of
elongation or compression possible, or within the limits
of elasticity; -- called also Young's modulus.
Modulus of rupture, the measure of the force necessary to
break a given substance across, as a beam, expressed by
eighteen times the load which is required to break a bar
of one inch square, supported flatwise at two points one
foot apart, and loaded in the middle between the points of
support. --Rankine.
[1913 Webster]