A (usually rigid), flat, rectangular measuring or drawing device with graduations in units of measurement; a straightedge with markings.
A person who rules or governs; someone or something that exercises dominion or controlling power over others.
To beat with a ruler (as a traditional school punishment).
An analog calculator consisting of three interlocking strips marked with logarithmic scales, such that multiplication, division etc. can be performed by the equivalent of addition and subtraction.