[ansonhoyt]

The ARRL Ham Radio License Manual, 3rd edition, section 1.1 explains the term:

> How did “amateur” become “ham”? The real answer is unknown! Even before radio, telegraphers referred to a poor operator as a ham. Perhaps this was derived from a poor operator being “ham-fisted” on the telegraph key — an operator’s “fist” referred to his or her distinctive style over the wires. With all radio stations sharing the same radio spectrum in the early days, commercial and military operators would sometimes refer to amateurs as hams when there was interference. Regardless, amateurs adopted the term as a badge of honor and proudly refer to each other as “hams” today.

While you'd buy the latest 5th edition from the ARRL [1] to prepare for the exam, the older 3rd edition is freely available online [2].

[1] https://www.arrl.org/ham-radio-license-manual

[2] https://macaloney.blogspot.com/2019/06/how-to-prepare-for-ha...