If you pant, you breathe quickly and loudly with your mouth open, because you have been doing something energetic. She climbed rapidly until she was panting with the effort. see also pants
the noise made by a short puff of steam (as from an engine) breathe noisily, as when one is exhausted; "The runners reached the finish line, panting heavily"
[ 'pant ] (verb.) 14th century. Middle English, modification of Middle French pantaisier, from Vulgar Latin phantasiare to have hallucinations, from Greek phantasioun, from phantasia appearance, imagination; more at FANCY.