security是secure的名词形式，本意是safety；protection的意思；金融中的本意应该是抵押品，担保品（保护证券持有者的权益），比如证券发行者给了证券持有者一份纸质文件将其作为担保(security)，证券就作为证券持有者的所有权的一种凭证（an instrument of investment in the form of a document (as a stock certificate or bond) providing evidence of its ownership）
词源：Legal sense of “property in bonds” is from mid-15c.; that of “document held by a creditor” is from 1680s

多谢！