(phrasal verb) (slang) to behave in a very friendly, flattering, or kind manner to someone higher than you in order to get a benefit
Sarah always kisses up to her boss, because she’s trying to get a promotion and a raise.
A: Who’s your professor this semester?
B: Professor Ornstein.
A: Oh, he’s really tough. If you want to get a good mark, you’d better start kissing up to him!
B: How should I do that?
A: Start by telling him he is the best professor you’ve ever had. Then keep going….
William was angry because he didn’t get promoted to manager, even though he had kissed up to the owner of the company for years.