All four words, "cough", "admit", "disclose", and "sing", are verbs.
Here's a breakdown:
* Cough: A physical action of expelling air from the lungs.
* Admit: To acknowledge or confess something.
* Disclose: To reveal or make known something that was previously secret.
* Sing: To produce musical sounds with the voice.
Therefore, the commonality between these words is that they are all actions or processes described by verbs.