What is the noun in My hearing so good that I can hear armies of ants marching?

The noun in the sentence "My hearing is so good that I can hear armies of ants marching" is hearing.

Here's why:

* Hearing is the subject of the sentence, and subjects are typically nouns.

* Hearing is the ability to perceive sound, which is a tangible thing.

Let me know if you'd like to try another sentence!