What is "imperial bushel"

Imperial \Im*pe"ri*al\, a. [OE. emperial, OF. emperial, F. imp['e]rial, fr. L. imperialis, fr. imperium command, sovereignty, empire. See Empire.]

1. Of or pertaining to an empire, or to an emperor; as, an imperial government; imperial authority or edict.

   The last That wore the imperial diadem of Rome.
   --Shak.

2. Belonging to, or suitable to, supreme authority, or one who wields it; royal; sovereign; supreme. ``The imperial democracy of Athens.''
   --Mitford.

   Who, as Ulysses says, opinion crowns With an imperial voice.
   --Shak.

   To tame the proud, the fetter'd slave to free, These are imperial arts, and worthy thee.
   --Dryden.

   He sounds his imperial clarion along the whole line of battle.
   --E. Everett.

3. Of superior or unusual size or excellence; as, imperial paper; imperial tea, etc.

   Imperial bushel, gallon, etc. See Bushel, Gallon, etc.

   Imperial chamber, the, the sovereign court of the old German empire.

   Imperial city, under the first German empire, a city having no head but the emperor.

   Imperial diet, an assembly of all the states of the German empire.

   Imperial drill. (Manuf.) See under 8th Drill.

   Imperial eagle. (Zo["o]l.) See Eagle.

   Imperial green. See Paris green, under Green.

   Imperial guard, the royal guard instituted by Napoleon I.

   Imperial weights and measures, the standards legalized by the British Parliament.