"Sprig tail" is a unique term that may not have many direct synonyms, but there are several related phrases and terms that can be used interchangeably. Some options include "brush tail," "tufted tail," "bushy tail," "feathery tail," "fluffy tail," and "plumed tail." Each of these terms adequately describes a tail that contains thick, lush strands of fur or feathers, making them ideal alternatives to "sprig tail." Additionally, you could also consider using more general terms like "thick tail" or "bushy appendage" depending on the context. Regardless, these synonyms and similar phrases make it easy to accurately describe the unique appearance of a "sprig tail" in your writing.