When sailors returned home from a voyage, they would be paid off in one lump sum. Most would then stay at shoreside establishments catering to sailors until their money ran out. When that happened, the owners ("crimps") would advance money so that the sailors could purchase more food, rum and "companionship" at that establishment at inflated prices.
For centuries, it was common practice to give a sailor one month's wage in advance when they signed on for a voyage. This advance was intended for the purchase of needed clothing and other gear before departure. Often times this money went to repay the crimps. By the middle of the 19th century, captains were paying the advances directly to crimps for providing crew, bypassing the poor sailor. Thus, most sailors would be working only for their food for the first month of a voyage.
This food was supposed to mostly consist of salt beef. Food provisioners, whenever they could get away with it (which was quite often), would substitute much cheaper and chewier salt horse for a portion of the salt beef. Even when salt beef was provided, some of it would have been in casks for years before being given to the crew to eat, making it as hard to chew as salt horse. It was quite usual for the crew to refer to their food as salt horse when it was bad, or dead horse if it was worse than bad.
So, for the first month the sailors were working only for their food, their salt horse, their dead horse. They were said to be "working off their dead horse," and were referred to as dead horses themselves. Flogging them to get them to work harder was a waste of energy. Thus, "you can't beat a dead horse" to get any more work done.
Seamen Smith is still working off a dead horse until we hit our next port.
by Mike January 29, 2005
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Something which one is not supposed to beat.
Dead horses won't get up no matter how much you hit them. Honest. Leave the carcass alone, please. Ew.
by Lady Chevalier May 12, 2005
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In case you don't feel like reading all the babble up there, a dead horse when said in a forum means that the topic has been done so many times before- so be more original k?
This horse has been beaten so many times, it's already dead.
by Nycus March 13, 2005
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A name for a person who declines an invitation to a social situation or event, without a valid excuse. Usually occurs when someone is invited out but decides to stay in for the night simply because they are "kind of tired".
Mike: Hey Brad I'm on my way I'll be at your place in 20 mins to start pregaming.

Brad: Where is Will? I thought he said he was coming?

Mike: Nah he is being a dead horse. He decided to stay in by himself and solojerk to Netflix instead. F him

Brad: F it
by Skydiver November 19, 2014
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An amateur bowling team from the New Founders League at Double Decker Lanes in Rohnert Park, California. They didn't really do that well in their first season (Winter 2010)
Man: "Hi Rose, How did your team do in league last night?"

Rose: "We beat A Dead Horse... again."
by curly666 April 15, 2011
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Rap crew from SF bay during the early 2000's
Dead Horses in the house tonight I hear they brought hott fire
by Tim L from Nevada City November 7, 2008
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