There are several synonyms for the term "big bird". Some of the common synonyms that are used to refer to birds that are large in size include "giant bird", "huge bird", "massive bird", "colossal bird", and "monstrous bird". These terms are frequently used in the scientific community to refer to birds such as eagles, condors, and ostriches that are known for their large size. Other synonyms for big bird that are more commonly used in casual settings include "jumbo bird", "mega bird", and "whopper bird". These terms are often used by birdwatchers and nature enthusiasts when describing the size of a particular species of bird.