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.
This is why your ears pop. Sometimes people suffering from ETD get crackling noises in their ears or deafness. The deafness is usually temporary and is as a result of the normal flexible ear drum, or tympanic membrane, becoming stiff as a result of the increased pressure behind it. The ear drum is therefore unable to move when a sound wave hits it and so the sound is muffled when it is heard. The crackling is due to the mucus moving within the middle ear. It is the blockage of the Eustachian tube that causes pain in the ears when flying as the changes in air pressure make it difficult for the pressure across the ear drum to equalise. This causes the ear drum to be stretched, which is painful.