impound & under lock and key

Japan Times Online, July 14の記事タイトル Pens called weapons, impounded を見てもさっぱり意味が分からなかったので記事を読みました。
More than 200 American-made pens have been held in a warehouse at Chubu airport since April 2011 because Nagoya Customs has categorized them as defensive weapons.
Customs officials say the fountain and pens, produced by U.S. firearms and knife makers, will remain under lock and key until they are approved for importation as weapons.
...
But Gifu Prefecture-based Yamahide Cutlery Mfg. Inc., which imported about 1,000 of the pens between March 2008 and April 2011, is questioning why such approval is all of sudden required for stationery items.
なるほどこれでタイトルの意味は良く分かりました。知らない単語 "impounded" の意味も "under lock and key" と同じだと推測できます。
・Collins English Dictionary:
a.to seize (chattels, etc) by legal right
b.to take possession of (a document, evidence, etc) and hold in legal custody
Example: But Customs frequently impound carloads of booze despite drivers ' protests that it is for personal consumption.
・Vocabulary.com: take temporary possession of as a security, by legal authority: “The customs agents impounded the illegal shipment”
"under lock and key" は慣用句の様なのでこれも辞書で確認しておきます。
・Cambridge English Dictionary: locked away safely: Her jewellery is securely under lock and key at the bank.
-- If a person, especially a criminal, is under lock and key, they are being kept in a place from which they cannot escape, usually a prison.
・Dictionary.com: under lock and key, securely locked up: The documents were under lock and key