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trooper (n.)
[trooper 词源字典]
1630s, "soldier in a cavalry troop," from
troop
(n.) +
-er
(1). Extended to "mounted policeman" (1858, in Australia) then to "state policeman" (U.S.) by 1911.
[trooper etymology, trooper origin, 英语词源]
[trooper 词源字典]