From the root ג־מ־ל(g-m-l), in the qatélet pattern usually forming nouns relating to diseases but not always ((e.g. טַיֶּסֶת(tayéset, “squadron”), שַׁלֶּכֶת(shalékhet, “fall (autumn leaves)”) and צַנֶּרֶת(tsanéret, “pipeline”)) and not in this case.