Pixieish is a word that describes a playful, mischievous, and fairy-like personality. Its antonyms would be words that describe a more serious or subdued personality. This could include words like solemn, serious, restrained, subdued, and modest. A person who is not pixieish might be more conventional, traditional, or conformist. They may also have a more reserved, pragmatic, or practical demeanor. Ultimately, antonyms for pixieish will be words that convey a sense of seriousness, practicality, and conventional behavior, rather than playful imagination and spontaneity.