A ham or ham actor is one who struts his piece upon the stage to little effect, a fifth-rate artiste of the sort that P G Wodehouse said “couldn’t play the pin in Pinafore”. He may fail because he is an unskilled amateur, though the word is more often applied to a thespian who overacts in a theatrical or ranting way to compensate for his poor grasp of technique or to upstage his fellow actors.
The term is American and dates from the nineteenth century. Where it comes from has been the subject of more inventive etymology than you can shake a stick at. It’s said to be from Hamlet’s advice to the actors (“O, it offends me to the soul to hear a robustious periwig-pated fellow tear a passion to tatters, to very rags, to split the ears of the groundlings”), though why it had to wait 300 years to appear is not explained. A related idea is that the word comes from the title of the play, which is one that amateurs frequently perform badly. Others argue it’s from a Cockney pronunciation of amateur, hamateur, but that would put the origin on the wrong continent.
In the 1860s, ham began to be used in America for somebody who was stupid, clumsy or worthless, especially an untalented prize fighter. This is most likely to have been borrowed from ham-handed or ham-fisted, meaning a person with large hands that fancifully resembled the prepared ham of a pig, hence clumsy.
In a separate development in the 1870s, ham began to be applied to variety performers, who were looked down on by “legitimate” actors. It was also used for incompetents within the profession generally:
Ham — is the most derisive word in the professional vocabulary, and if you wish to lose the friendship of anyone in the business call him a “ham,” and that settles it. A person who can do nothing at all, can not speak his lines properly or is any way bad in his calling, is denominated a “ham”.
Cincinnati Enquirer, 7 Sep. 1879.
In this sense, it’s almost certainly an abbreviation of the slightly older hamfatter:
“When Dellaven proposed this concert business, I told him I was no ham-fatter, and — ” “Ham-fatter?” “Yes. Ham-fatter. That’s the name we give a man in our profession who is a poor performer.”
Nashville Union and American, 6 Nov. 1874.
The consensus is that the source lies with low-paid performers in minstrel troupes, who had to make do with ham fat for cleaning off make-up after a performance rather than a more expensive cream. It seems likely that a mental association grew up with the existing sense of ham for a clumsy or useless person. Another link may have been hambone, slang for a third-rate minstrel performer; this is said — not entirely convincingly — to come from trombonists in such troupes using ham fat to grease the slides of their instruments, slangily known as bones.
Ham later became a term for an amateur radio enthusiast. There has been much controversy about where the term comes from, but it seems certain that it’s connected to ham in the sense of clumsy. With that meaning it was used in the 1890s by US railway telegraphers to describe ill-trained, slow and inaccurate Morse-code operators. It seems to have been adopted early in the next century as an inverted badge of honour by early radio experimenters, who also communicated using Morse code.