As a noun:
* The duck waddled across the pond, quacking happily.
* I saw a flock of ducks swimming in the lake.
* We had duck for dinner last night.
* She used a duck to hold the door open. (This is a slang term for a doorstop)
As a verb:
* I ducked under the low-hanging branch.
* He quickly ducked behind the wall when he heard the noise.
* She ducked her head as she walked through the doorway.
* The boxer ducked to avoid the punch.
As an idiom:
* Don't duck your responsibilities.
* I'm going to duck out of this meeting early. (This means to leave quickly and quietly)
* He tried to duck the question, but the reporter persisted. (This means to avoid answering a question)
In a humorous way:
* "Quack, quack," said the duck.
* My dad always tells me, "Don't be a duck and just go for it!"
The meaning of "duck" will change depending on the context of the sentence.