Dictionary.net

An order signed by a judge that directs owners of private property to allow the police to enter and search for items named in the warrant. The judge won't issue the warrant unless she has been convinced that there is probable cause for the search -- that reliable evidence shows that it's more likely than not that a crime has occurred and that the items sought by the police are connected with it and will be found at the location named in the warrant. In limited situations the police may search without a warrant, but they cannot use what they find at trial if the defense can show that there was no probable cause for the search.

In law, a warrant granted by a justice of the peace to a constable to enter the premises of a person suspected of secreting stolen goods, in order to discover and if found to seize, the goods. Similar warrants are granted to search for property or articles in respect of which other offences are committed, such as base coin, coiners tools, also gunpowder, nitro-glycerine, liquors, etc., kept contrary to law. Under the Federal Constitution the law of search-warrant required that the property sought and the place to be entered and searched must be specifically described. Before 1776, Writs of Assistance were issued by royal order in the Colonies, giving officers of the crown the power to search and invade the homes of the people in very indiscriminate and outrageous fashion. The reaction against such tyrannical invasion of privacy gave us our present well-hedged law, under which the homes of citizens may not be so invaded, and search-warrants may not issue without probable cause, indemnity bond in civil cases, and a specific description of the place and the property involved in the process.

Warrant authorising a search for stolen goods, &c.