Definition of interest:

part of speech: verb

To concern; to affect; to engage, as the attention or affections; to give or have a share in.

part of speech: noun

Influence over others; benefit; good; regard to private profit or advantage; concern; share; price paid for the use or loan of money- the sum lent being called the principal, the interest for a year on £ 100 the rate, and the principal and interest the amount.