"Kissing up to" is a phrase used to describe someone who is trying to gain favor or approval from a person of authority or influence through flattery or excessive compliments. But, as with any other word or phrase in the English language, there are several synonyms that can be used to convey the same meaning. Some of these synonyms include "brown-nosing," "sucking up," "apple-polishing," "crawling," "groveling," "fawning," and "buttering up." These words may have varying levels of intensity or formality, but all communicate the idea of insincere or excessive flattery in order to gain favor or benefit.