When a word ends in ~거리다, it means that whatever is being done, is being done repeatedly. So: 흔들다 = to shake 흔들거리다 = to continually shake Although you can’t just add ~거리다 to every word to give it the meaning of ‘being repeated.’ Only certain words can use this ending, and you should consider words ending in ~거리다 as a separate word, not just a normal word with a special ending. In addition, some words only end in ~거리다 – that is – other than their ~거리다 form, there is no other way that they can be used. For example: 머뭇거리다 = to continually hesitate 두리번거리다 = to continually look around.

The suffix of " -거리다" or "대다" is usually used when making a verb by adding 의태어(mimetic word). Like this, 둥실둥실--둥실거리다, 둥실대다. 말랑말랑--말랑거리다, 말랑대다. 반짝반짝--반짝거리다, 반짝대다, etc. It shows a state or looking(shape) of the action or act of the mimetic word, repeated continuously.