1.
to shake; to rock
To move something back and forth or up and down.
肩を揺すって起こした。
I woke him by shaking his shoulder.
木を揺すって実を落とした。
I shook the tree to make the fruit fall.
母が赤ちゃんをやさしく揺すっている。
The mother is gently rocking the baby.
2.
to extort; to blackmail
Colloquial usage meaning to extort money by threatening.
金を揺すられた。
I was extorted for money.
弱みを握られて揺すられている。
Someone has something on me and is blackmailing me.
秘密をばらすと脅して大金を揺すり取ろうとした。
He tried to extort a large sum of money by threatening to reveal the secret.
揺する is a transitive verb (他動詞). The intransitive pair is 揺れる (to shake, to sway).
ASPECT ({ている}):
揺すっている indicates an ongoing action of shaking something.
COMMON PATTERNS:
- 肩を揺する - to shake someone's shoulder
- 木を揺する - to shake a tree
- 揺り起こす - to shake someone awake
- 揺すり落とす - to shake something off
揺する VS 揺れる:
- 揺する (transitive): someone shakes something
- 揺れる (intransitive): something shakes/sways on its own
NOTE ON SENSE 2:
The slang meaning "to extort" comes from the image of shaking someone down for money. This usage is informal.