Noah Webster's New International Dictionary of the English Language

1. (n.) One who, or that which, multiplies or increases number.

2. (n.) The number by which another number is multiplied.

3. (n.) An instrument for multiplying or increasing by repetition or accumulation the intensity of a force or action, as heat or electricity. It is particularly used to render such a force or action appreciable or measurable when feeble. See Thermomultiplier.