Because the Chinese word "knife" is the homophone of the English pronunciation of US dollar.
dollar
UK?['d?l?]?US?['dɑl?]?
n. US dollar
Phrases:
1. Zimbabwean dollar?Zimbabwe dollar
2. Half dollar?cent; US dollar nickel; Kennedy's head; half dollar
3. Straits dollar ? Lat currency; Malaysian and Singapore dollars; Lat Koh National Treasury banknotes
4. Malayan Dollar? Malayan dollar
5. dollar index? U.S. dollar index
Extended information
Synonyms:
1. greenback
English?['gri?nb?k]?American?['grin'b?k ]?
n. U.S. dollar; greenback
Example:
Many?people?see?gold?as?the “anti-dollar”, ?so?if?the?greenback?does?well,?they?have less?incentiveto own?bullion.?
Many consider gold to be “anti-dollar,” so if the dollar performs well , they have no incentive to own gold.
2. American dollar
n.[Financial] US dollar
Example sentence:
At?that time,?both gold and? silver?were?used to?support?the?value of the?American?dollar.?InEurope, however,?only?gold?was?used.?
At that time, both gold and silver dollars were used To support the US dollar, while in Europe, only gold is used to support the national currency.