Big yawn is a rather casual and informal term that is often used to indicate boredom or fatigue. Some examples of antonyms for big yawn include invigorating, stimulating, exciting, energetic, and lively. These words convey a sense of enthusiasm and interest, in stark contrast to the dullness of a big yawn. Other antonyms that may be used to describe the opposite of a big yawn include engaging, captivating, fascinating, enthralling, and thrilling. Essentially, any term that denotes excitement, passion, or interest can be considered an antonym for big yawn, which is often associated with a sense of listlessness and disinterest.