To Shake, To Jolt
transitive verb, godan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means shake so the verb vocab version is to shake.
ゆさぶる
The reading comes from 揺る.
コウイチが木を揺さぶったので、ビエットは枝に掴まった。
Viet held onto the branch because Koichi shook the tree.