What is the answer to verbals ending in -ing and used only as nouns are?

Verbals ending in -ing and used only as nouns are called gerunds.

Here's a breakdown:

* Verbal: A word that is formed from a verb but functions as a different part of speech.

* Gerund: A verbal that ends in -ing and functions as a noun.

Examples of gerunds:

* Swimming is my favorite way to exercise. (Subject of the sentence)

* I enjoy reading novels. (Object of the verb "enjoy")

* She is good at dancing. (Prepositional object)

Key point: While all gerunds end in -ing, not all words ending in -ing are gerunds. Some can be present participles (verbs used as adjectives, e.g., "the running water").