Merriam-Webster's Collegiate® Dictionary, 11th Edition
SWELTER
I. verb (sweltered; sweltering)
Etymology: Middle English sweltren, frequentative of swelten to die, be overcome by heat, from Old English sweltan to die; akin to Gothic swiltan to die
Date: 14th century
intransitive verb to suffer, sweat, or be faint from heat, to become exceedingly hot , transitive verb to oppress with heat, exude ,
II. noun
Date: 1851
a state of oppressive heat, welter , an excited or overwrought state of mind ; sweat