Definition from Wiktionary, the free dictionary
- To give up, surrender, or yield (e.g. a weapon), usually by placing it on the ground.
- The police urged the gunman to lay down his weapon.
- Lay down your arms.
- To intentionally take a fall while riding a motorcycle, in order to prevent a more serious collision.
- He laid down his brand-new Harley-Davidson to avoid the oncoming bus.
- To specify, institute, enact, assert firmly, state authoritatively, establish or formulate (rules or policies).
- Let's lay down the rules right at the beginning, so we are consistent.
- You've got to lay down the law with that boy.
- To stock, store (e.g. wine) for the future. See also lay by.
- To sacrifice, especially in the phrase "to lay down one's life."
- (intransitive, nonstandard, proscribed) To lie down; to place oneself in a reclined or horizontal position, on a bed or similar, for the purpose of resting.
- I feel a bit ill, so I'm going to go lay down for a while.
Derived terms 
To surrender or yield (a weapon) by placing it on the ground