• gappy hour,
• bappy hour,
• nappy hour,
• jappy hour,
• uappy hour,
• yappy hour,
• hzppy hour,
• hsppy hour,
• hwppy hour,
• hqppy hour,
• haopy hour,
• halpy hour,
• ha-py hour,
• ha0py hour,
• hapoy hour,
• haply hour,
• hap-y hour,
• hap0y hour,
• happt hour,
• happg hour

The adjective form of "happy hour" is "happy-hour".

The plural form of "happy hour" is "happy hours".

The singular form of the word "happy hour" is "happy hour". The word itself does not change when used in singular or plural form.