Correct spelling, explanation: the word horniness is derived from the adjective horny, which describes a state of being sexually excited or aroused. In English, when forming nouns from adjectives, we often add the suffix -ness to create abstract nouns that describe a quality or state of being. When forming nouns from adjectives that end in -y, you generally change the -y to -iness. For example: happy -> happiness, sleepy -> sleepiness. So, horny becomes horniness. Using hornyness would be considered incorrect in standard English.

Definition of horniness:
Noun, sexual excitement or sexual attraction
His constant flirtatious remarks revealed his underlying horniness.
The steamy scenes in the movie heightened the audience’s sense of horniness.

Collocations with horniness:
Some of the most commonly used collocations include:
1. Feelings of horniness: describes the general sensation or emotion of being sexually aroused.
After watching the romantic movie, she couldn’t shake off her feelings of horniness.
2. Intense horniness: indicates a strong or powerful feeling of sexual arousal.
The novel’s explicit scenes led to an intense horniness that she had never felt before.
3. Overwhelming horniness: describes a feeling of sexual arousal that is difficult to control or resist.
He tried to focus on his work, but the overwhelming horniness made it challenging.
4. Sudden horniness: refers to an abrupt onset of sexual arousal.
Out of nowhere, she experienced a sudden horniness while chatting with him.

Incorrect spelling, explanation: the word hornyness is considered incorrect because it does not follow the standard rules of English word formation. In English, when forming abstract nouns from adjectives that end in -y, we typically change the -y into an -i and add the suffix -ness. For example, from the adjective happy, we form the abstract noun happiness. The correct form of the adjective horny when transformed into an abstract noun should be horniness. Hornyness is just a mistake and we should remember that.