Webster's Revised Unabridged Dictionary · 1913

Fm

Fm , proper noun

the symbol for the element Fermium.

FM , noun

[Frequency Modulaiton.]

A method of transmitting radio signals by modulating the frequency of the carrier wave; -- opposed to AM (amplitude modulation), in which the signal modulates the amplitude, rather than the frequency of the carrier wave. [acron.]

Fm , proper noun

The chemical symbol for Fermium, a transuranic element.