swel ‧ ter /ˈsweltə $ -ər/ BrE AmE verb [intransitive]
[ Date: 1400-1500 ; Origin: swelt 'to die, become unconscious because of heat' (11-20 centuries) , from Old English sweltan 'to die' ]
to feel extremely hot and uncomfortable:
Crowds of shoppers sweltered in the summer heat.