Most undesigning refers to someone who is straightforward, honest, and lacks deceitful intentions. The antonyms for this phrase would be deceitful, cunning, and crafty. A deceitful person would be someone who is intentionally dishonest and manipulative. A cunning person is someone who is skilled in deceiving others or achieving their own goals through sly tactics. Crafty refers to someone who is smart and resourceful, but also unscrupulous in how they achieve their aims. These terms are the opposite of most undesigning, as they suggest that the person in question has hidden agendas and is not to be trusted.