In (one's) (own) interest noun phrase
The phrase can be rewritten as "in the interest of one" or "in one's best interest".
In order to bring advantage or benefit to somebody
It would be in your interest if you are proficient in the second language.
The people have supported policies in their interest.
A plan, project, development, or course of action that seems to have no meaningful, desirable, or useful conclusion
To be beneficial to someone or something
The phrase dates back from the early 1700s
1. Soneone tends to speak in unkind and cruel way that is likely to upset or hurt someone else.
2. The fossil tooth of a shark
1. Many people doesn't want to make friends with Sue because she has a serpent's tongue.
2. A: 'My thesis will center on a serpent's tongue.' B: 'A serpent's tongue? What does it mean?' A: 'A serpent's tongue means the fossil tooth of a shark.'