I agree with Kaori-san.
なびく originally means "some soft and long things like hair, draps, leaves, willow leaves, rice plants, wheat plants, or seaweeds are moving softly in soft winds(or some stream)".
Google-image-serach it with "なびく", then you will understand it visually.
https://www.google.co.jp/imghp?hl=ja&tab=wi