1810, member of a gang of murderers and robbers in India who strangled their victims, from Marathi thag, thak cheat, swindler, Hindi thag, perhaps from Sanskrit sthaga-s cunning, fraudulent, possibly from sthagayati (he) covers, conceals, from PIE root *(s)teg- cover (see stegosaurus).
It may also occur in one ear or both ears. The most common reason for muffled hearing is conductive hearing loss that can be caused by a variety of factors or medical conditions including a build up of ear wax and ear infections. In most cases, however, it is treatable and does not lead to permanent hearing damage.
1 Hearing reduced, soft, muffled or even tinny.  Tinnitus heard at various levels. This can be a roar, whooshing and or a 'tuning fork' type ringing sound. Rumbling, droning, cracking, popping, humming.. the list of descriptive sounds goes on and on. It varies from person to person.