What is Bill Of Sight?

Legal Definition
English commercial law. When a merchant i's ignorant of the real quantities or qualities of any goods consigned to him, so that he is unable to make a perfect entry of them, he is required to acquaint the collector or comptroller of the circumstances and such officer is authorized, upon the importer or his agent making oath that he cannot, for want of full information, make a perfect entry, to receive an entry by bill of sight, for the packages, by the best description which can be given, and to grant a warrant that the same be landed and examined by the importer in presence of the officer; and within three days after the goods have been so landed, the importer is required to make a perfect entry. See stat. 3 & 4 Will. IV. c . 52, ยง24.
-- Bouviers Law Dictionary
Legal Definition
When an importer of goods is ignorant of their exact quantity or quality, so that he cannot make a perfect entry of them, he may give to the customs officer a written description of them, according to the bast of his information and belief. This is called a "bill of sight."
-- Black's Law Dictionary
Legal Definition
A lawful customhouse entry of goods which withholds full information from the importer.
-- Ballentine's Law Dictionary