Diffide is an uncommon word that means to lack confidence or be hesitant. Synonyms for diffide include hesitate, waver, vacillate, falter, dither, or have doubts. These words convey the sense of being uncertain or indecisive, and they can be used interchangeably depending on the context. Other synonyms for diffide include balk, scruple, demur, or recoil, which convey the sense of being resistant or hesitant for moral or ethical reasons. They all express a similar lack of decisiveness or confidence, but each word has its own nuance and connotation. It is important to choose the appropriate synonym that fits the context and tone of the writing.