n. (1889 in Fraser, 1: 208) Food [ben-tō 弁当 lunch (package), written lit. as ‘speech, hit’ < MChin; o- 御 (< NJ) is honorific] A meal packed in a decorated, partitioned box.
(Cannon, Garland. 1996. The Japanese Contributions to the English Language: An Historical Dictionary.)
“Bento” originates from the Southern Song slang term 便當 (pinyin: biàndāng), meaning “convenient” or “convenience.” When imported to Japan, it was written with the ateji 便道, 辨道, and 辨當. In shinjitai, 辨當 is written as 弁当.
In the 20th century, the term was reimported to modern Mandarin Chinese, rendered as 便當 (pinyin: biàndāng), where it retains its older meaning of “convenient” and also refers to bento in mainland China and generic boxed lunches in Taiwan.