The Collaborative International Dictionary
Grand chop
Chop \Chop\, n. [Chin. & Hind. ch[=a]p stamp, brand.]
Quality; brand; as, silk of the first chop.
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A permit or clearance.
Chop dollar, a silver dollar stamped to attest its purity.
chop of tea, a number of boxes of the same make and quality of leaf.
Chowchow chop. See under Chowchow.
Grand chop, a ship's port clearance.
--S. W. Williams.
Wiktionary
grand chop
n. A ship's port clearance.