束, originally tied firewood/wood/timber, serves as a phonetic component to form characters. 束 is compound ideograph.
In modern Chinese, 束 means:
1.to bind. to tie
2.a bundle, a cluster
3.restraint
束 serves as a phonetic component to form characters.
Characters formed by the phonetic component 束
速 涑 梀 觫 趚 殐 sù
凁 捒 shù
竦 悚 sǒng
疎 踈 shū
Among all these characters, just two are commonly used, and the rest are very rarely used.
See also the component 耒