the GNU version of the Collaborative International Dictionary of English
adj. Going at a gallop; progressing rapidly.
The Century Dictionary and Cyclopedia
n. The action of a horse that gallops; a running at a gallop.
Proceeding at a gallop; hence, figuratively, advancing rapidly; making rapid progress: as, a galloping consumption (that is, a consumption that proceeds rapidly to a fatal termination).
Word Usage
"He was 53 years old from what they called galloping pneumonia."