interestyoudaoicibaDictYouDict[interest 词源字典]
interest: [15] The Latin verb interesse meant literally ‘be between’ (it was a compound of inter ‘between’ and esse ‘be’). It was used metaphorically for ‘be of concern, be important, matter’, and appears to have been borrowed into Anglo-Norman as a noun, meaning ‘what one has a legal concern in or share of’. English took this over in the 14th century as interesse, but it gradually changed over the next hundred years or so into interest, mainly due to the influence of Old French interest ‘damage’, which came from the third person present singular form of the Latin verb.

The main modern sense ‘curiosity’ developed towards the end of the 18th century.
[interest etymology, interest origin, 英语词源]
interest (n.)youdaoicibaDictYouDict
mid-15c., "legal claim or right; concern; benefit, advantage;" earlier interesse (late 14c.), from Anglo-French interesse "what one has a legal concern in," from Medieval Latin interesse "compensation for loss," noun use of Latin interresse "to concern, make a difference, be of importance," literally "to be between," from inter- "between" (see inter-) + esse "to be" (see essence).

Compare German Interesse, from the same Medieval Latin source. Form in English influenced 15c. by French interest "damage," from Latin interest "it is of importance, it makes a difference," third person singular present of interresse. Financial sense of "money paid for the use of money lent" (1520s) earlier was distinguished from usury (illegal under Church law) by being in reference to "compensation due from a defaulting debtor." Meaning "curiosity" is first attested 1771. Interest group is attested from 1907; interest rate by 1868.
interest (v.)youdaoicibaDictYouDict
"to cause to be interested," c. 1600, earlier interesse (1560s), from the noun (see interest (n.)). Perhaps also from or influenced by interess'd, past participle of interesse.