What does Boxing Day have to do with boxing?
early 15c., medical term for "gurgling heard in the abdomen," a native, echoic formation, or ultimately from Latin gurguliare, perhaps via Dutch, German gurgeln. Extended (non-anatomical) use, in reference to water over stones, etc., is first recorded 1713. "This phenomenon of long specialized use before becoming a part of the general vocabulary is often found in English" [Barnhart]. Related: Gurgled; gurgling. As a noun from early 15c.