Which term is synonymous with insincere flattery?

The term synonymous with insincere flattery is "obsequious." This word describes behavior that is overly eager to please or ingratiate oneself with someone in authority, often to a degree that comes across as insincere or excessively flattering. People who are obsequious tend to use flattery as a means to gain favor or advantage, reflecting a lack of genuine respect or admiration. Such behavior typically aims at self-serving ends, aligning it with the idea of insincere flattery.

The other options do not convey this same sense of insincerity in flattery. "Complacent" refers to a sense of self-satisfaction without awareness of potential dangers or deficiencies, lacking the direct connection to flattery. "Transparent" indicates openness and clarity, opposing the notion of insincerity. "Altruistic" describes a selfless concern for the well-being of others, which stands in stark contrast to the concept of flattery driven by ulterior motives. Overall, "obsequious" elegantly captures the essence of insincere flattery, differentiating it from the other terms in the context of the question.