According to the Merriam Webster Dictionary, "flattery" means false or excessive praise. "Complimenting," on the other hand, means offering respect or admiration for the other person. Where flattery is insincere, a compliment is offered with earnestness.

Flattery has a number of synonyms, each with its own nuance that gives flattery its negative connotation. One synonym for flattery, adulation, depicts admiration carried to an extreme. Blarney is a skillful form of flattery meant to charm the other person. Fawning seeks out the other person's approval or attention by acting ingratiatingly. A flatterer uses blandishment to coax or cajole the other person into doing something, or to wheedle something out of the other person.

The synonyms for complimenting have a more positive undertone than those for flattery. Offering acclaim, for instance, applauds the other person or proffers fervent support. To exalt the other person means to honor or to glorify him. Saluting the other person is a means of welcoming that person and offering him your goodwill. Additional synonyms for "compliment" include commend, commemorate and congratulate.

Flattery makes use of a person's need to be praised, or to have his ego stroked. A flatterer can use this need to manipulate others into doing his bidding. Flattery tells an angry man how wonderful he is for being strong and knowing what he wants, or tells a jealous woman how great it is that she's protecting her relationship with her lover or husband. The flatterer, then, controls others by constantly feeding them words they want to hear about themselves. Complimenting, by contrast, honors the other person with kind words. It builds relationships rather than tearing them down or undermining them. Compliments are sincere and use words that are heartfelt. Complimenting also has the side effect of making the giver feel good about herself.